An Extended Historical View of Congressional Party Polarization
David W. Brady
Hahrie Han
Stanford University
Department of Political Science
Encina Hall
Stanford, CA 94305
[email protected]
[email protected]
Working paper prepared for presentation at Princeton University, Dec. 2, 2004.
Introduction
The question of why congressional parties have polarized so much since the late 1970s is a topic
that has received much scholarly attention in recent years. Existing explanations include accounts of
endogenous institutional change that have contributed to increased partisanship in Congress, and accounts
of exogenous political change that helped alter the configuration of congressional parties. Research
focusing on endogenous institutional change argues that the House reforms of the 1970s strengthened the
power of party leaders, thus making it easier and more profitable for parties to act as cohesive voting
blocs (Rohde 1991; Van Houweling 2003), and that changes in voting procedures on the House floor
contributed to more partisan voting behavior (Roberts and Smith 2003). The bulk of the research
focusing on the role of exogenous political change looks at changing characteristics of congressional
districts, including the advent of redistricting (Carson et al. 2003; Cox and Katz 2002), the increase in
income inequality across districts (McCarty, Poole, and Rosenthal 2002), the change in population
(Stonecash, Brewer, and Mariani 2002), and, perhaps most of all, the decline of the one-party South
(Rohde 1991, Black and Black 2002; Theriault 2003).
One interesting feature of this body of research is that it focuses particularly on the sources of
congressional party polarization beginning in the late 1970s, thus intimating that the recent period of
congressional polarization is unique and should be explained as such. This paper offers an alternative
perspective on this question that begins by redefining the historical time period over which polarization
occurs. We start by examining trends in congressional party polarization throughout the latter half of the
nineteenth century and the twentieth century. In both the House and the Senate, the historical data shows
that the recent period of polarization is, in fact, a readjustment to patterns of polarization that prevailed
throughout most of congressional history. In fact, instead of the recent period of polarization, the
bipartisanship of the immediate post-WWII period is the unusual historical period in both the House and
the Senate. The mean difference between party medians is at its lowest just after WWII (Schickler 2000)
and the polarization that follows in the 1970s and 1980s is distinct only in comparison to the post-WWII
period.
2
We argue that the bipartisanship of the 1950s sheds light on the re-emerging polarization of the
1970s and 80s. In the 1950s, parties—in the electorate, in Congress, and in presidential elections—took
similar positions on key issues such as race, national defense, and even the role of government in the
immediate post-WWII era as the class-based, New Deal era partisanship faded. Partisan issue distinctions
between the two major parties blurred, and did not re-emerge until the polarizing issues of the 1960s and
70s (such as race) redefined partisan lines. Interestingly, this re-emergence of partisanship in the 1960s
became clear in the electorate and in presidential elections as voters and presidential candidates sorted
themselves into parties, but did not appear in Congress until the late 1970s and 1980s.
Our interpretation of polarization focuses on this lag in congressional party polarization. Why
did congressional party polarization take so long to re-emerge? We examine the rise of cross-pressured
members of Congress, who were caught between their constituencies and their parties. As the national
parties began to re-polarize in the 1960s, Democrats with conservative constituencies and Republicans
with liberal constituencies were caught in the middle. Many of these cross-pressured members managed
to stay in office by creating a personal vote, which insulated them from the re-appearance of polarizing
issues in the 1960s. Members of Congress could stay in office with the personal vote even if the national
party no longer represented the dominant ideological preferences of the district. It was not until these outof-step legislators were replaced by members of the opposite party who better aligned party and district
preference that partisan lines in Congress became redefined.
The paper proceeds as follows. The first section examines the implications of looking at
historical patterns of party polarization in both the House and the Senate. We show that polarization in
the late twentieth century is essentially a return to historical patterns of polarization that have prevailed
for most of U.S. history. Instead, it is the immediate post-WWII era that is unusual because of its high
levels of bi-partisanship. Thus, we examine some of the unique historical features of this time period,
including the decline of New Deal’s class-based politics and the rise of the personal vote in congressional
elections. The second section examines the return to polarization after the bi-partisan era of the 1950s.
We argue that both the House and the Senate lagged behind the electorate and presidential elections in
3
returning to historically prevalent levels of partisanship. Thus, we redefine the question of polarization to
ask why congressional voting took so long to re-polarize. The third section looks more closely at the role
of cross-pressuring in explaining this lag in congressional party polarization. We argue that the personal
vote insulated members of Congress from emerging national partisan tides in the 1960s. It was not until
these members retired or were electorally defeated that polarization emerged in Congress. Understanding
these patterns of delayed electoral replacement is crucial to understanding the emergence of polarization
in Congress in the late twentieth century.
Part I: Identifying Historical Patterns of Polarization
Most research on congressional party polarization begins by trying to explain the rise in
partisanship in the final decades of the twentieth century. This approach ignores historical patterns of
polarization in Congress that can provide important insights into understanding polarization of the
modern era. This section elucidates those historical patterns, and identifies the unusual period of bipartisanship around the 1950s. Then, we explore the unique features of the immediate post-WWII era to
better understand the subsequent rise in partisanship in the 1970s and 1980s. We find that the return to
polarization in both the House and the Senate lagged behind the return to polarization in the electorate
and in presidential elections. This leads us to redefine the question of polarization in the twentieth
century to include a broader historical view.
Historical Polarization in Congress
Throughout most of United States congressional history, parties in the House and Senate have
been relatively polarized. Figure 1 plots the difference between Republican and Democratic party
medians, as measured by first-dimension DW-Nominate scores in both the House and the Senate.1 In
both chambers, party polarization peaked in 1895 and plummeted to its lowest level in 1947 and the early
1
This graph is similar to one found in Shickler 2000.
4
1950s. 2 The return to polarization in the final decades of the twentieth century does not look as unusual
when placed in this historical context. The party differences during this era are lower than they were in
the late 19th century. Instead, what becomes clear is that the era of bi-partisanship in the immediate postWWII era is the unusual era in American history.
INSERT FIGURE 1 ABOUT HERE
The unique features of partisanship in the 1950s are highlighted by an alternative measure of
polarization that examines the degree of overlap between the two parties. Parties can either be polarized,
with high levels of internal cohesion and low levels of intra-party overlap, or they can be convergent, with
low levels of internal cohesion (wider distributions) and high levels of intra-party overlap. Figure 2
presents two hypothetical models of partisanship. In the top figure, the two parties are relatively
polarized, with very little overlap between them; there are very few Republicans who overlap with the
most conservative Democrats and vice versa. In contrast, the bottom figure depicts considerable overlap
between the two parties. Although the most liberal Democrats and the most conservative Republicans
remain distinct from each other, partisanship in the middle of the two-party distribution is indistinct. The
more conservative Democrats look quite similar to the more liberal Republicans, and the more liberal
Republicans look like the more conservative Democrats.
INSERT FIGURE 2 ABOUT HERE
We used this model to explore the degree of congressional party overlap over time. We used two
different measures of ideology: first-dimension DW-Nominate scores (1867-1999), and Americans for
2
It is worth noting that the difference between party medians in the Senate was consistently lower than the House
from the late 1800s to the early 1950s. In addition, a relatively large decline in the difference between party
medians in the Senate occurs in the early 1930s, and persists through the 1950s. See footnote #4 for more on this
topic.
5
Democratic Action (ADA) scores (1947-1999). Both ranking systems rate the liberalism (or
conservatism) of elected officials based on their roll call voting records. Using these scores, we could
identify how liberal or conservative members were relative to other members of their party. We
identified the cut points for the 10%, 25%, and 50% (the median value) most conservative Democrats,
and the 10%, 25%, and 50% most liberal Republicans. The bottom of Figure 2 shows the hypothetical
placement of the cut point for the 10% most liberal Republican on a DW-Nominate scaling. In this case,
the most conservative Democrats are more conservative (with higher ideological rankings) than the 10%
most liberal Republicans. The shaded area shows the area of overla p. By thus by identifying these cut
points, we can observe the number of members from the opposite party who fall into the overlap region.
In other words, how many Democrats are more conservative than the 10% most liberal Republican? And
how many Republicans are more liberal than the 10% most conservative Democrats? As an example, in
1947 (80th Congress), the most conservative 10% of Democrats had DW-Nominate scores higher than
0.10. To identify the degree of overlap with Republicans, we counted the number of Republicans who
had DW-Nominate scores lower than 0.10. Figure 3 shows the degree of overlap in each Congress from
1867-1999. For the purposes of brevity, we only show the distribution using DW-Nominate scores.3
INSERT FIGURE 3 ABOUT HERE
These graphs demonstrate an unprecedented level of overlapping voting in both the House and
the Senate in the immediate post-WWII era. Looking at the distributions of DW-Nominate scores, it
becomes clear that there was almost no House party overlap prior to the 1940s. In the Senate, there was
some overlap in the 1920s and the 1930s, but it was relatively mild compared with the immediate post
3
Although we do not include the graphs showing ADA overlap, the results are the same. The only difference is that
ADA scores do not begin until 1947 and they show a greater degree of non-south overlap among Democrats in the
1950s and 1960s than DW-Nominate scores.
6
WWII era.4 By the 1940s and 1950s in both the House and the Senate, the degree of partisan overlap
spiked upwards. By 1947, almost 45% of House Democrats were more conservative than the 10% most
liberal Republicans. The numbers peaked around 1963, when over 55% of House Democrats were more
conservative than the 10% most liberal House Republicans, and almost a third of Democrats were more
conservative than the 25% most liberal Republicans. 10% of House Democrats were more conservative
than even the median Republican member of the House. Among Republicans, levels of overlap grew
sharply between 1947 and 1955, and persisted at high levels until the early 1970s when the number of
members in the overlap region began to decline. In the Senate, the numbers were highest in the late
1960s. In 1969, 19% of Democrats were more conservative than the 10% most liberal Republicans, and
19% of Republicans were more liberal than the 10% most conservative Democrats. This level of overlap
persisted through the late 1970s, when it began to decline in both chambers, and lasted in weaker form
through the 1980s. Like Roberts and Smith (2003), we find that for both parties in the House,
polarization (or low levels of partisan overlap) re-emerges in the 1980s. We performed the same analysis
looking only at non-Southern states to see if the partisan overlap was merely an artifact of one-party
politics dominant in the South before the Civil Rights Movement. We find that although the degree of
overlap decreases among Democrats, the mid-twentieth century still emerges as a unique period of high
partisan overlap. Among Republicans, we also find that high levels of partisan overlap persist even when
we take the Southern states out of the analysis.
Two important points emerge from this examination of historical patterns of polarization in
Congress. First, the patterns of polarization in the House and the Senate have been markedly similar
throughout most of history. This is true using several other measures of partisanship , including party
4
Like the decline in the difference between party medians, partisan overlap appears in the Senate before it appears
in the House. We are currently gathering and analyzing some data to better understand this phenomenon. We
hypothesize, however, that patterns of inter-state migration may have had a similar (but earlier) impact on the Senate
that redistricting had on the House. In the House, after the 1960s, states often created congressional districts that
were highly partisan by drawing district lines around partisan neighborhoods. In the Senate, although redistricting
was not an issue, the migration of certain groups of people into a state had the similar effect of changing the
constituency base of the member of Congress. Some data show that patterns of northern migration into the South
around the 1930s-1950s could have affected the rise of Southern conservatism (Polsby 2004), and thus facilitated the
growth of partisan overlap in the Senate before the House.
7
voting scores (e.g. Rohde 1991; Hurley and Wilson 1989) and party unity scores (e.g. Brady, Cooper, and
Hurley 1979). By all measures, historical trends in the Senate are quite similar to those in the House.
These parallel trends in the House and the Senate have important implications for our understanding of
the sources of congressional party polarization. As previously noted, existing explanations for
polarization in the House can broadly be divided into two categories: sources of endogenous institutional
change, and sources of exogenous political change. The endogenous institutional changes cited as
sources of polarization in the House, however—for example, the 1970’s reforms strengthening the power
of parties, the Subcommittee Bill of Rights (1973), and the Committee Reform Amendments (1974)—did
not happen simultaneously in the Senate.5 This implies that exogenous political changes had an impact
on levels of polarization in Congress, influencing both chambers simultaneously. In other words, looking
solely at the endogenous institutional changes in the House, or focusing on explanations like redistricting
that do not occur in both chambers does not capture the full story.
Second, this examination of historical patterns in the House reveals the importance of
understanding the immediate post-WWII era to better understand polarization in the latter decades of the
twentieth century. By understanding the sources of the unusual decline in partisanship after WWII, we
can better understand the sources of a return to polarization in the 1970s and 1980s. Previous scholars
have recognized the unique levels of bi-partisanship in the immediate post-WWII era (e.g. Brady, Cooper,
and Hurley 1979; Schickler 2000; Jacobson 2000; 2003; Poole and Rosenthal 1984), but none of the
authors have sought to link the decline in the immediate post-WWII era to the subsequent rise of
polarization in the late 1970s and 1980s. Instead, most research has sought to explain the final decades of
the twentieth century as the unique period. Because the 1950s were the unusual period in the history of
polarization in Congress, however, scholarship on the sources of polarization in the twentieth century
should explain both the decline in polarization after WWII, and the subsequent return to polarization in
5
Although the Senate experienced some rules changes in the early 1970s, they did not have nearly the same effect as
changes in the House (Sinclair 1988; 1989; Rohde 1991, p. 178; Shepsle 1989). In her analysis of committee
assignments in the Senate, Sinclair (1988) notes that, “The [redistributive provisions of the 1970 Reorganization
Act] were modest in design and even more modest in impact” (293). In other words, the impact of the 1970
Reorganization Act in the Senate was relatively limited, not greatly altering the composition of Senate committees.
8
the 1970s and 1980s. Thus, we turn next to an exploration of the unique political characteristics of this
time period.
Features of the Immediate Post-WWII Era
To better understand the high degree of partisan overlap in the immediate post-WWII era, we
discuss two important historical trends. First, during the 1950s, the two-party system was characterized
by broad agreement between Democrats and Republicans on key national issues, such as race, national
security, and the role of government in society. Second, after WWII, congressional elections became
more independent, as members of Congress learned to win office independent of party. This section
discusses each of those features in turn.
During the immediate post-WWII era, voters demonstrated considerable overlap between the two
parties for the first time, as the party system shifted away from the New Deal parties preceding the war.
From 1930 to the mid 1940s, political parties divided clearly over economic issues and the extent of
American involvement in Europe and the world. Parties in this period were clearly defined: most voters
voted for the same party at the Presidential and congressional levels (Burden and Kimball 2002), party
platforms exhibited distinct positions on economic and international involvement issues (Ginsberg 1972),
and elected officials from each party demonstrated hardly any ideological overlap with each other. Socioeconomic class was particularly potent in defining partisanship. The People’s Choice, a study of voters in
Sandusky, OH in 1940, found that “being in a low-income group, a Catholic, or an urban resident, all
predisposed a voter toward the Democrats; being in a high-income group, a Protestant, or a rural resident
predisposed a voter toward the Republicans” (Lazarsfeld 1960). Robert R. Alford (1964) used Michigan
Survey Research Center data and Gallup and Roper polls to analyze class voting from 1936 to 1960. His
findings show that from 1936 to the 1950s, voting differences between classes were consistently high.
Berelson, Lazarsfeld, and McPhee (1954) found in their 1948 study of Elmira that the swing to Truman
which won him the election over Dewey came from those to whom class issues were salient. Judson
James (1969) concluded that “This fifth party system not only reversed the majority/minority party role s
9
of the Republicans and Democrats, but also more nearly than any previous two-party system, it had a
basis in class conflict” (45). The New Deal system that characterized parties before and through WWII,
in other words, was undoubtedly defined in the ele ctorate and in Congress along class lines.
After WWII, however, the differences characterizing Democrats and Republicans in the New
Deal system began to disappear. The 1948 election was the last election in the class-based New Deal
party system. V.O. Key writes,
“Perhaps in the election of 1936 the party division most nearly coincided with
differences of income and occupation. That coincidence declined as class relevant
questions faded from the forefront, and in 1952 and 1956, Republicans won substantia l
support in the lower-income groups.” (Key 1958, 274)
Likewise, Campbell, Converse, Miller and Stokes (1960) computed an index of state polarization and
found that the correlation between occupational status and the partisan vote fell over the 1948-1956
period. Socio-economic class, in other words, declined as the defining feature of political parties in the
1950s. Interestingly, however, as class divisions between parties became less clear, a new foundation for
defining the parties did not emerge.
Instead, during the 1950s, we see considerable overlap between the two parties on key national
issues. The election of Eisenhower, a popular war-time hero, inspired significant levels of cross-party
voting during the 1950s, and levels of differentiation between Democrats and Republicans began to erode.
On key issues, such as national security, Democrats and Republicans were quite similar: Democrats like
Kennedy matched Republicans in their Cold War stances. On issues related to Civil Rights, the Southern
wing of the Democratic party kept the party from adopting civil rights stances until 1964. Thus, until the
early 1960s, it was not clear if Republicans or Democrats would be more supportive of civil rights.
Similarly, as the class-based New Deal system of parties began to disappear, differences between
Democrats and Republicans on issues related to the role of government weakened.
To examine these historical trends, we looked at a set of issues over the 1948-2000 period to
determine the timing of change in the electorate. We use the National Election Studies (NES) crosssectional studies from 1948 to 2000. Because questions on issue opinions were not asked consistently
10
over time, we went through each cross-sectional study and created an opinion index for each respondent
on three key dimensions. In creating the scales, we followed methodology established in Stimson (1991).
These issues are:
1. National Defense: This index encompasses respondents’ views on U.S. policy towards
Communism and Communist countries, and levels of military power or defense spending. The
scale runs from –1 to 1, with –1 indicating a more hawkish position, and 1 indicating a more
dovish position. 0 implies neutrality.
2. Race/Civil Rights: This index captures respondents’ views on issues regarding race and civil
rights. This includes views on the Civil Rights movement, school integration, busing, and the
federal government’s role in supporting minorities. The scale ranges from -1 to 1, with –1
implying less government intervention, and 1 implying greater government intervention. 0
implies status quo.
3. Role of Government: This index includes questions about the role of government in providing
social welfare. It encompasses questions about government’s role in supporting full employment,
health care, housing and utilities, social security, food stamps, and other government services.
This scale also runs from –1 to 1, with –1 indicating less government, and 1 indicating more
government. 0 is status quo.
We recoded any question in the NES cross-sections that pertained to one of the three issues above (see
Appendix 1 for the questions included in each scale). We then created a composite score for each
individual that represented the mean of her answers on the –1 to 1 scale. We could then aggregate these
individual scores to create mean scores for Republicans versus Democrats in each presidential election
year. Figure 4 shows the mean differences between parties over time on issues related to race, defense,
and role of government.
INSERT FIGURE 4 ABOUT HERE
11
These graphs reveal a basic historical pattern: the voters converged on key issues in the 1950s, but
patterns of polarization began to reemerge in the 1960s.6 On defense issues, the differences between the
parties were zero in the 1950s, and only began to rise thereafter. On race issues, the difference between
voters from each party hovers around zero and only begins to rise in 1964. On issues related to the role of
government, the differences between parties fluctuate more, but we nevertheless witness a relative
convergence between voters from each party in the mid-1950s, and a subsequent divergence. In other
words, it becomes clear that on these three major issues of the immediate post-WWII period, the
electorate was not divided along clear partisan lines. Issues which had previously determined the partisan
basis of the electorate were fading in importance as cues to mass voting behavior.
As levels of partisanship in the electorate and in Congress declined in the 1950s, members of
Congress learned to become more independent of party in their attempts to seek re-election. The rise of
the “personal vote” is well-documented in political science scholarship through studies of the incumbency
advantage (Alford and Brady 1993; Erikson 1972; Ansolabehere, Snyder, and Stewart III 2000; Gelman
and King 1990; Jacobson 1987; Cain, Ferejohn, and Fiorina 1987). Beginning in the 1950s, the
incumbency advantage began to rise and increased more or less consistently until its peak in 1988, when
incumbents had a 12% electoral advantage over non-incumbents. One commonly used method of
measuring this is the slurge, or the mean value of the sophomore surge and the retirement slump. 7
Measures of slurge over time show that the sharpest rise in the incumbency advantage came in the late
1950s and 1960s. Simultaneously, the percentage of districts with split partisan results at the presidential
and congressional levels moves from zero at the start of the 20th century, to a dramatic rise between 1948
and 1972 (Burden and Kimball 2002). With respect to the election of Eisenhower in 1952 and 1956, the
level of split ticket voting was understandable as voters from both parties chose a popular war hero for
6
Although a precise comparison is not possible, we find that these results are consistent with Stimson’s (1991)
results. See Stimson, figures 4.4 and 4.5.
7
The sophomore surge is calculated as the difference between the winning vote share of candidates running as
incumbents for the first time, versus their winning vote share in the previous election. The retirement slump is the
mean decrease in the party’s vote from an election in which an incumbent was running, to an election in which the
incumbent retires and the seat is open.
12
President. However, in the 1960s, as issues related to race, the Vietnam War, and later the environment
emerged as dividing issues, voters still split their tickets. Both of these patterns—the rise in the
incumbency advantage and the rise in split districts—demonstrate the increasing tendency of
Congressional elections to be subject to forces other than partisanship. Research shows that there is, in
essence, a trade-off between the effect of the personal vote (as represented by the incumbency advantage)
and the effect of partisanship in determining electoral outcomes (Ansolabehere and Snyder 2002).
Instead of relying on parties to secure re-election, members of Congress in the post-WWII began to rely
on other factors.8
Throughout the immediate post-WWII era, then, partisan lines blurred in both Congress and the
electorate. Levels of bi-partisanship were higher than ever before in the House and the Senate, and the
New Deal system of parties began to fade in the electorate. Democrats and Republican were not very
differentiated on key national issues like national security, civil rights, and the role of government.
Members of Congress, in turn, learned to win office on their own, relying less on party and more on other
independent factors. What changed? How did this system give way to the partisanship of the latter
decades of the twentieth century?
Part II: The Historical Lag in Congressional Party Polarization
Following the unique bi-partisanship of the immediate post-WWII era, partisan lines began to
reappear in the electorate and in presidential elections throughout the 1960s. The social movements of
the 1960s, striking demographic changes, and polarized presidential elections prompted a redefinition of
partisan lines. Both the House and the Senate, however, were slow to respond to these changes. As
shown in Figures 1 and 3, polarization in Congress did not reappear until the late 1970s or early 1980s.
This section discusses this lag in the re-emergence of congressional party polarization.
8
A rich body of research has explored the sources of the personal vote. See, for example, Cain, Bruce E., John
Ferejohn, and Morris P. Fiorina. 1987. The Personal Vote: Constituency Service and Electoral Independence.
Cambridge: Harvard University Press, Fiorina, Morris P. 1977. Congress: Keystone of the Washington
Establishment. New Haven: Yale University Press.
13
In addition to plotting the mean differences between parties on three key issues, Figure 4 also
shows the trajectory of polarization in Congressional voting, as measured by the difference in DWNominate scores by party. It is clear that on defense issues, the partisan differences in the electorate were
growing in the early 1960s and again in the 1980s, but remained relatively constant in Congress
throughout the 1960s and 1970s. On race issues, partisanship in the electorate grows steadily starting in
1964, but it is not until 1972 that congressional voting begins to polarize. On the issues related to the role
of government, partisan differences in the electorate rise rapidly in the early 1960s and stay consistently
high (with the exception of 1972), even though polarization in Congress does not appear until the 1980s.
In each case, it appears that voters were using party to sort out policy choices long before aggregate levels
of congressional voting reflected such polarization.
To understand the re-emergence of polarization after the 1950s, we start by examining existing
explanations for House party polarization in the current literature. As previously noted, the parallel trends
in polarization in the House and the Senate intimate that explanations focusing solely on endogenous
institutional change may not tell the whole story. The key exogenous political changes that scholars cite
as sources of polarization in the House are: (1) the impact of redistricting on creating more polarized
congressional districts (Carson et al. 2003; Cox and Katz 2002), (2) the impact of changing populations
within the districts (Stonecash, Brewer, and Mariani 2002), (3) the impact of changing levels of income
inequality (McCarty, Poole, and Rosenthal 2002), and (4) the impact of political change in the South
(Rohde 1991; Black and Black 2002). Clearly, we can rule out redistricting as an explanation for
polarization in the Senate, since reapportionment of congressional districts has no impact on state
boundarie s. The remaining three explanations for increased polarization make the same basic point: some
exogenous political shock altered the electoral bases of the parties, creating greater intra-party
homogeneity and greater inter-party heterogeneity. The change in these electoral coalitions prompted
greater congressional polarization.
The key exogenous shocks, however—changing trends in income inequality, changing
demographics, and change in the one-party South—occurred primarily in the mid-1960s. In developing
14
their arguments about the changing constituency bases of the parties, McCarty, Poole, and Rosenthal
(2002) 9 , Stonecash, Brewer and Mariani (2002), Rohde (1991), and Black and Black (2002) find some
common ground in a set of exogenous shocks occurring in the 1960s that led to a reconfiguration of
constituency bases of the parties. Perhaps most prominently, the adoption of the 1964 Civil Rights Act,
and the selection of Barry Goldwater as the Republican nominee in the 1964 presidential election marked
clear divergence of the parties on civil rights. The subsequent Voting Rights Act in 1965 sparked the
enfranchising of black voters throughout the South. Also in 1965, Congress passed the Immigration and
Nationality Act Amendments of 1965, reinforcing increasing levels of legal immigration to the United
States that had begun to rise in the mid 1940s. Finally, begin ning in the 1960s and particularly in the
1970s, economic inequality began to rise (Piketty and Saez 2001; Stonecash, Brewer, and Mariani 2002,
64-74). As noted by multiple authors, the 1960s were a tumultuous time of much social and political
change that redefined the political parties.
Despite the tumult of the 1960s, House and Senate party polarization did not begin to appear until
the late 1970s; this is true even though presidential elections and partisanship in the electorate reflected
the changes. Many authors, including Stonecash, Brewer and Mariani (2002) and Black and Black
(2002), note that despite the changes in the 1960s, the demographic changes take some time to take effect.
We agree that this is the case, but argue that there were also institutional characteristics that insulated
congressional parties from exogenous changes and slowed the pattern of change. In fact, looking at levels
of black voter registration, it is clear that the key changes were in the 1960s: in 1960, black voters
comprised 10.6% of the pool of registered voters in the South, and by 1968 that number had jumped to
16.5%, a number that held relatively constant for the next twenty years until 1988 (Stonecash, Brewer,
and Mariani 2002, 55). The demographic changes, thus, took hold and congressional parties still lagged
behind the change.
9
This point also comes from a talk by Keith Poole, “Economic Inequality and Political Polarization,” April 22,
2004, Stanford, CA.
15
Presidential elections did not follow the same patterns as Congress and, instead, paralleled
changes in the electorate. The highly bi-partisan elections of Eisenhower in the 1950s gave way to the
turbulent electoral processes of the 1960s. The Johnson-Goldwater elections of 1964 and the NixonHumphrey elections of 1968 were both divisive, prompting party identification to become a better
predictor of vote choice. After the 1968 convention, in fact, liberal activists in the Democratic party
garnered sufficient power to pressure the party into reforming the nomination process (Polsby and
Wildavsky 1980). These reforms, which eventually occurred in the Republican Party as well, forced
presidential candidates to cater to more extreme primary voters. To win a party’s nomination, in other
words, presidential candidates had to win the support of a narrow band of primary voters. A series of
studies, however, have shown that these party activists are often not representative of the larger party’s
interests (Jackson, Brown, and Bositis 1982; McClosky, Hoffman, and O'Hara 1960; Nexon 1971; Verba
and Nie 1972; Soule and McGrath 1975; Kirkpatrick 1976). 10 Presidential politics, thus, began to evince
clear patterns of divergence between parties, particularly among party elites.
Despite these changes in the electorate and in presidential elections, congressional voting
remained surprisingly immune from this increase in partisanship. To examine this assertion, we
performed a logit regression of the probability of voting Democratic in presidential and congressional
elections on the issue indexes of electorate opinions on race, role of government, and defense used earlier
in the paper. The model is as follows:
Pr(Dit =1) = Φ(α + β1 Role it + β2Raceit + β3Defenseit + error it )
Where,
Dit = Probability of voter i voting Democrat in the election t
Role it = Voter i’s score on the role of government index in election t
Race it = Voter i’s score on the race index in election t
Defense it = Voter i’s score on the defense/national security index in election t
10
Other studies have found that presidential nomination activists take electability of the candidate into account as
much as ideological congruence (see esp. Stone and Abramowitz 1983; Stone, Rappoport, Abramowitz 1992).
Although the primary voters may weight general election electability in making their vote choices, however, this
does not preclude the fact that the new nominating system forces candidates to appeal to a group that is not the same
group they must appeal to in the general election.
16
If our assertion is that congressional elections remained immune from the resurgence of
partisanship in the 1960s, then predicted probabilities from this regression should show that voters’
congressional vote choice should remain less partisan throughout the 1960s, thus lagging behind
presidential vote choice. Figure 5 graphs the predicted probabilities from this regression. 11
INSERT FIGURE 5 ABOUT HERE
In calculating the predicted probabilities, the issue indexes are set to –1; in other words, this hypothetical
voter consistently holds conservative views on issues related to race, defense, and the role of government.
The predicted probabilities represent the percentages of conservative voters that are likely to vote
Democratic. The figure shows that while presidential and congressional elections paralleled each other
until the early 1960s, they began to diverge thereafter. In the first two post-WWII elections,
conservatives were quite likely to vote Democrat for President and Congress, from 32.2% in the 1952
House election, and 25.9% in the Senate election. In fact, in 1952, more conservatives are predicted to
vote for Stevenson than for Democratic House and Senate candidates. After 1960, however, the
percentage of conservative voters predicted to vote for a Democratic presidential candidate never reaches
20% and only in 1964, 1968, and 1976 does it reach double digits. In 1964, 1972 and from 1980 onward,
the number of conservatives voting Democratic for President is predicted to be below 10% and averages
less than 5%. In contrast, conservative votes for House candidates is predicted to be 18.5% in 1956 and is
over 20% from 1960-1984 with the average being over 27%. Not until the 1984 election does the percent
conservative voters predicted to vote Democratic in House elections fall to 12.8%; and through 1996, it
averages about 11%. Similarly, in the Senate, from 1960-1980, the percent of conservative voters voting
for a Democratic Senator is at least 20% and usually is higher. It is not until 1980 that the percent of
conservatives voting for a Democratic Senate candidate begins to drop.
11
See Appendix 2 for the summary statistics from the regression.
17
This lag in congressional party polarization adds another dimension to understanding the rise of
polarization in the late 1970s and 1980s. The data shows that congressional party polarization took
substantially longer to re-emerge than polarization in the electorate and at the presidential level. While
presidential candidates and voters re-sorted themselves into parties around the polarizing issues of the
1960s, members of both the House and the Senate lagged behind. Congressional elections thus
differentiated themselves from presidential elections , and after the 1950s, partisanship in the Congress
was distinct from partisanship in the electorate. This casts the rise in congressional polarization in the
1970s and 1980s in a new light: it was a step behind the return to polarization in presidential elections and
in the electorate.
Part III: Why Did Congressional Party Polarization Take So Long to Emerge?
The previous section examined the timing of historical change in polarization and revealed a lag
in congressional party polarization. Despite tumultuous social and political changes in the 1960s,
congressional party polarization did not emerge until the late 1970s and early 1980s. This presents us
with an altered historical perspective. Instead of asking why congressional parties polarized in recent
decades, we ask why parties in Congress took so long to re-polarize despite changing trends in the
electorate and at the presidential level. Our approach to understanding this question focuses on the rise of
members of Congress cross-pressured between their district and their national party. In this section, we
start by discussing the role of cross-pressuring in sustaining levels of bi-partisanship in Congress beyond
the 1950s, then demonstrate how polarization in Congress re-emerged as members who had been crosspressured between their geographic constituencies and their party retired or were electorally defeated.
The Rise of Cross-Pressured Legislators
As the national parties grew increasingly distinct throughout the 1960s, we argue that the
divergence of congressional elections cross-pressured a group of legislators. These legislators were
pulled in one direction by their constituents, and in another direction by their national party. For example,
18
a Border State Democrat like Jim Jones of Oklahoma was pulled in a more conservative direction by his
district, but in a more liberal direction by the Democratic party. Likewise, Northeastern Republicans
during the 1960s were pulled in a more conservative direction by their national party, but in more liberal
direction by their districts. Pulled in two opposite directions by their party and their constituency, these
members had a strategic dilemma: how could they balance the countervailing pressures they faced while
still winning re-election?
Caught between their parties and their constituencies, we argue that these cross-pressured
members had several options that range from being very partisan to non-partisan. First, the most partisan
response that members can have to cross-pressuring is to simply switch parties. We count this as a
partisan response because members who are cross-pressured and switch parties subsequently reduce the
dissonance between their parties and their constituencies, thus enabling them to more comfortably vote
with the national party. For instance, Democrats from conservative districts can simply switch to the
Republican party as the national Democratic party becomes too liberal. The second (middle) option is for
the members to try to balance the cross-pressures between their party and their district. This could lead to
cross-pressured members being slightly out of step with both their parties and their constituencies. For
example, cross-pressured Republicans who are trying to balance the cross-pressures will be too
conservative for their constituencies, but too liberal for their parties (and vice versa for Democrats). This
balancing can encompass a range of behaviors, ranging from members Gillis Long (D-LA) who voted
sometimes with his own party, and other times with the Republicans, to members like Phil Gramm (DTX) who voted consistently with the Reagan Republicans. Members like Gramm represent the third
option, which is the least partisan response that members can have: they can simply vote with the opposite
party. We count this as the least partisan response because these members are bucking the pressures of
their national party to vote more consistently with the preferences of their constituents. Thus, by our
measure of partisan overlap outlined in the second section of this paper, we would expect that crosspressured members are more likely to fall in the overlap region. Finally, there is a fourth option that does
19
not lie on the continuum of most partisan to least partisan responses. This fourth option is for members to
simply leave office through retirement or electoral loss.
The middle option—balancing—is particularly interesting because these members had to find
ways to compensate for being slightly out-of-step with both their parties and their constituencies. We
hypothesize that the personal vote played a critical role in helping these members to stay in office.12
Because of the growing levels of the personal vote during the 1960s, a disproportionately high subset of
these legislators could stay in office despite being out of step with their party and their constituencies. In
other words, by insulating members of Congress from rising partisan tides in the 1960s, the personal vote
helped cross-pressured members who were out-of-step with the changing partisan tides of the 1960s stay
in office. This is also true for cross-pressured members who voted with the opposite party—the source of
their personal vote could have been their issue-based alignment with their constituency. In both cases,
however, the personal vote played an important role in shielding cross-pressured members from the
polarizing trends of the 1960s. Cross-pressuring and the personal vote, thus could have helped delay the
re-emergence of polarization in Congress.
Based on our argument, then, we expect that members who are cross-pressured have higher
personal vote scores than members who are not cross-pressured, since they have to rely more on the
personal vote to help them win re-election. Similarly, we expect that rates of switching parties and voting
with the other party are higher for cross-pressured members. To examine this, we identify the members
who were cross-pressured. We identified Democrats who had conservative constituencies and
Republicans who had liberal constituencies. Consistent with previous work, we measured constituency
liberalism by looking at three-year moving averages of presidential vote in the district or state (CanesWrone, Brady, and Cogan 2002; Ansolabehere, Snyder, and Stewart III 2001; Erikson and Wright 1997).
12
By “personal vote,” we are referring to the portion of the candidate’s vote margin that is attributed to factors
personal to the candidate, not the candidate’s party. Thus, a candidate can generate a personal vote from a variety of
sources —including constituency services, pork barrel politics, or issue-based alignment with the district—but the
sources of the candidate’s personal vote are always located in the candidate’s district. This independent relationship
that congressional candidates had with their geographic constituencies played a crucial role in insulating members of
Congress from rising partisan tides in the 1960s.
20
Liberal constituencies were identified as areas that had voted more than 55% Democratic. Conservative
constituencies were identified as areas voting more than 55% Republican. Cross-pressured Democrats,
thus, were Democratic members who came from districts or states voting more than 55% Republican at
the presidential level. Conversely, cross-pressured Republicans were Republican members who came
from districts or states voting more than 55% Democratic at the presidential level. 13
The data is largely supportive of our argument. First, looking at party-switchers, we find that
there are sixteen cases of members who switch parties in the House over this time period, and three cases
of members who switch parties in the Senate (see Nokken 2000 for more discussion of these cases).
Among the 19 House and Senate members who switched parties, most are cross-pressured. However, it is
clear that changing parties is not a frequent occurrence. Instead, more cross-pressured members tend to
try to balance. To look more closely at members who try to balance the cross-pressures between their
constituencies and their parties, and members who opt to vote with the opposite party, we display the
results in Tables 1 and 2. Table 1 presents the results for the House and Table 2 presents the results for
the Senate. The results are shown for Republicans, Southern Democrats, and non-Southern Democrats.
INSERT TABLES 1 and 2 ABOUT HERE
The top line in Tables 1 and 2 shows the mean DW-Nominate scores for members who are crosspressured and members who are not cross-pressured. If our argument that these members contributed to
persistently low levels of partisan polarization in Congress is correct, then we would expect that crosspressured members are ideologically more moderate than their partisan counterparts not in the overlap
region. The results show that for both the House and the Senate, across both parties and both Southern
and non-Southern Democrats, our expectations are met. Among Democrats, the cross-pressured members
are less liberal, and among Republicans, the cross-pressured members are less conservative.
13
It is possible that there are members who are cross-pressured because their constituencies consistently vote with
the opposite party at the presidential level, but do not meet our 45-55 criteria. We use this standard of measuring
cross-pressuring, however, because it is a more conservative test.
21
The second part of Tables 1 and 2 looks specifically at members who seek to “balance” the crosspressures between their constituency and their party. We look here at the cross-pressured members who
stayed in office and compare them to non-cross-pressured members who stayed in office. We expect that
these cross-pressured members have a harder time securing re-election since they are less in line with
their national parties and their constituencies. Thus, we expect that they will have lower winning vote
margins. In addition, to help themselves maintain office, we expect that cross-pressured members will
build up a larger personal vote than members who are not cross-pressured. We examine slurge scores and
hypothesize that they should be larger for cross-pressured members. Looking at the results in Tables 1
and 2, it is clear that our hypotheses are supported. In all cases, cross-pressured members are winning
with lower vote margins, even though they have higher slurge scores than their non-cross-pressured
counterparts. The only exception to this is non-Southern Democratic Senators, whose average winning
vote margin is equal between cross-pressured and non-cross-pressured members. Even for these
Senators, however, the slurge score for cross-pressured members is higher than the slurge score for noncross-pressured members.
The third part of Tables 1 and 2 looks at the probability that members will vote with the opposite
party. We measure voting with the opposite party using our measure of partisan overlap outlined in the
second section of this paper. Here, we expect that cross-pressured members should fall into the overlap
region far more than non-cross-pressured members. Again, looking at the results in Tables 1 and 2, it is
clear that cross-pressured members are in the overlap region at higher rates than non-cross-pressured
members.
This look at the implications of being cross-pressured in the House and the Senate makes it clear
that cross-pressured members were more ideologically moderate than their non-cross-pressured
counterparts. In addition, they consistently had a larger personal vote than non-cross-pressured members.
This is consistent with our argument that cross-pressured members contributed to sustained levels of
bipartisanship in Congress throughout the 1960s and 1970s. Because the personal vote insulated crosspressured members from the changing national partisan tides in the 1960s and 1970s, these members
22
remained in office even as parties in the electorate and the presidential level re-polarized. Congressional
party polarization, thus, took longer to re-emerge.
Delayed Electoral Replacement
The previous section illuminated the role that cross-pressuring and the personal vote played in
delaying the emergence of partisan polarization in Congress around mid-century. Cross-pressured
legislators with the personal vote were resistant to the exogenous shocks to the political system in the
1960s, hewing to an ideological middle ground.14 How did polarization re-emerge, then, given the
persistently high levels of the personal vote that continue to exist? We argue that eventually, these
members retired or were defeated, and were replaced by members who brought district and party
preferences into alignment. As the replacement processes took effect over time, parties in Congress thus
became better sorted and more tightly defined, and partisan voting scores in Congress consequently rose.
The readjustment to historically prevalent patterns of polarization in Congress, thus, lagged behind
polarization in presidential elections and in the electorate because of the personal vote. Cross-pressured
members of Congress were able to maintain office, so their electoral seats did not sort themselves
properly into parties until these members retired or lost office.
This implies that patterns of electoral replacement—specifically of Democrats who are too liberal
for their districts being replaced by Republicans, and Republicans who are too conservative for their
districts being replaced by Democrats—contribute significantly to the rise in congressional partisanship in
the late 1970s and 1980s. This is a question of who loses and who replaces them. We argue that
Democrats who are too liberal for their districts (DW-Nominate residual scores less than zero) should be
replaced by Republicans who are more conservative, and Republicans who are too conservative for their
districts (DW-Nominate residual scores greater than zero) should be replaced by more liberal Democrats.
14
Previous research has documented the tendency of members who are more extreme than their districts to be more
likely to lose (Canes-Wrone, Brady, Cogan 2002). There remains a set of members who are somewhat out of step
with their dis tricts, yet continue to win office. Within that set, we expect that when Democrats who tend to be too
liberal and Republicans who tend to be too conservative lose, the seat will switch partisan control.
23
This results in a pattern of partisan replacement. Figure 6 shows how we use the DW-Nominate residuals
to examine this hypothesis. First, we regress the member’s DW-Nominate score on district presidential
vote. The resulting residual score acts as a measure of the member’s distance from the district. On the xaxis, we plot the residual score of the member who left office. The y-axis represents the corresponding
residual score of the replacement member. By our hypothesis, Democrats who are too liberal for their
district are replaced by Republicans who are more conservative and close to district preferences, and
Republicans who are too conservative for their district are replaced by Democrats who are more liberal
and still close to district preferences. Thus, we expect that the Democrat-to-Republican replacements will
lay the upper left hand corner; Republican-to-Democrat replacements should lie in the bottom right hand
corner. An important point to note is that the replacements are within 1.5 s.d. of the district preference—
they move in the expected direction, but still remain relatively close to what the district wants.
(INSERT FIGURE 6 ABOUT HERE)
An empirical look at the data from the 1950s to the 1990s shows the expected patterns to be true.
Figure 7 shows the data for the House and Figure 8 shows the data for the Senate. Both graphs reveal that
relative to district preferences, Democrats who are too liberal (residual scores less than zero) are replaced
by Republicans who are more conservative. Similarly, relative to district preference, Republicans who
are too conservative (residual scores greater than zero) are replaced by Democrats who are more liberal.
Importantly, we find that in the 1950s, the effects are the weakest. In terms of Democrat to Republican
replacements, we see multiple cases in which the Republican replacements remain too liberal for the
districts. In terms of Republican to Democratic replacements, we see the most cases where the
Democratic replacement is far more than one standard deviation away from the district. This is consistent
with our contention that the relationship between ideology and partisanship is considerably weakened in
the 1950s. It is only in the 1960s that we begin to observe the stronger relationships predicted by the
24
replacement hypothesis. In other words, the members sorted themselves out more clearly in the latter
decades.
(INSERT FIGURE 7 and 8 ABOUT HERE)
This sorting process was a crucial part of the re-polarization of political parties in Congress in the late
1970s and early 1980s. Legislators who had been elected into Congress during the murky partisan era
around mid-century stayed in office even after the parties re-polarized because of the personal vote. As
partisan lines re-emerged in the 1960s and 1970s, this contributed to a set of cross-pressured legislators
who were caught between the ideological pull of their district in one direction, and the party in the
opposite direction. Only when these members retired or were defeated did partisan lines re-emerge. As
new members who were sorted more appropriately by party lines were elected into Congress, levels of
partisanship that were more consistent with historical norms re-emerged.
We argue, thus, that this process of electoral sorting is crucial to understanding the return to
aggregate levels of polarization in both chambers. Congressional seats which had previously been
misaligned were sorted into the proper parties through this process of electoral replacement. Thus, the
changes in the ideological distribution of congressional seats should be best explained by electoral
replacement. As these seats sorted into the proper ideological alignments of party and constituency,
aggregate polarization begins to reemerge. To test the impact of electoral replacement on changing
ideological distributions within both chambers, we run the following regression model:
(∆ Ideology of Congressional Seat )i(t1-t0) = β0 +
β1
(∆ Constituency Preference)it +
β2
(# terms served) it0 +
β3
(Percent Black in District) it +
β4
(Income Inequality) it +
β5
(South) i +
[β6
(Redistricting) it0 +]
β7 −β 8 (Replacements)it + eit
25
Where,
•
Change in Ideology of Congressional Seat: This is measured by the change in the congressional
seat’s DW-nominate score. It is calculated as the difference between the DW-nominate score of
the current member and the DW-Nominate score of the member in the previous Congress. These
changing ideology scores refle ct the changing patterns of partisanship in Congress.15
•
Change in Constituency Preference: This controls for the fact that member ideologies may change
because members strategically position themselves to be consistent with changing ideologies
within their constituency. It is measured as the changing Republican presidential vote in the
geographic constituency (district for House, and state for Senate);16
•
The number of terms member i has served before Congress t: We include this as a proxy measure
for member conversion. In response to changes in the political environment—such as
redistricting and the changing constituency bases of the parties—members may adapt by altering
their voting patterns. Previous research shows that this could have contributed to the repolarization of parties in the 1970s (Theriault 2003). We control for this with a variable for the
number of terms the member has served, since previous research on member conversion shows
that Democrats move further left with each passing Congress, and Republicans move further right
(Jacobson 2003).
•
Percent Black of constituency i at time t is included to control for the possibility that a social
sorting process happens, as certain demographic groups tend to vote for one party over another
(Axelrod 1972; Axelrod 1986). It is measured as the percentage of the voting-age population in
the member’s geographic constituency that is black, according to Census measures.
•
Income Inequality: This is measured using the GINI coefficient, a commonly used measure of
income inequality (McCarty, Poole, and Rosenthal 2002). In the House, although district-bydistrict measures of income inequality are not available, we use state-by-state measures over time.
15
We also ran the analysis using ADA scores, and found the results to be the same.
We also ran this analysis using a cubic specification of the relationship between district presidential vote and DWNominate scores. We found that even with a cubic specification, the results remained the same.
16
26
The same measures are used in the Senate. In the 1950s, however, data on the GINI coefficient in
each state was not available, so we use median income in the state as a proxy; 17
•
Dichotomous variables for region and redistricting are included in the regression to test the
effects of alternate approaches to understanding polarization: the impact of the disappearance of
the one-party South (Rohde 1991; Black and Black 2002) and, in the House, the impact of
reapportionment (Cox and Katz 2002). In the analysis of the House, since the exact amount of
redistricting in each district cannot precisely be known, we ascertained for each district in the
appropriate years whether or not it had been reapportioned and gave it a value of 1 if it had and 0
if it had not. Although Carson, et al (2003) argue that looking at the extent of redistricting is a
better measure of whether or not redistricting had an effect, we contend that looking at districts
that had 50% or more population change biases the measure to find redistricting effects. This is a
more conservative test of the redistricting hypothesis;
•
Replacements represents two dichotomous variable for each the two possible types of partisan
replacement that could occur with respect to member i’s seat in Congress t:
β7 : Party switches (Rep-Dem or Dem-Rep)
β8 : Same party changes (Dem-Dem or Rep-Rep)
These are the key variables in our hypothesis. Our expectation is that the districts which switch
parties will show the greatest change in member ideology and, hence, alignment with the
district’s preferences. Specifically, Democrats who are too liberal for their districts are replaced
by Republicans (Dem-Rep is positive); Republicans who are too conservative for their districts
are replaced by Democrats (Rep-Dem is negative).
In this analysis, then, the null hypothesis is that controlling for all the alternative hypotheses about the
sources of polarization, the effect of delayed electoral replacement will disappear. The alternative
17
McCarty, Poole, and Rosenthal (2002) have an interesting paper exploring the linkages between partisan
polarization and income inequality. They find that from 1956-1996, self-identified partisan identification has
become more stratified by income. In our paper, we focus more on the relationship between characteristics of the
electorate and congressional and presidential vote choice. In this regression, however, we include measures of
income by district to explore variance in member partisanship based on income levels in the district.
27
hypothesis is that even when accounting for these alternative hypotheses, the alternative hypotheses will
remain, and the coefficient on the replacement variables will not be zero.
Table 3 shows the results for the House and Table 4 show the results for the Senate. Looking at
the Democrats in the House first, we see that across all decades, the effect of Republican-to-Democratic
seat changes have the most consistently significant effect. In all decades, the magnitude of the coefficient
is larger than any other coefficient, and it moves in the expected direction, negative. In other words, seats
that change from Republican to Democratic hands become significantly more liberal, thus sorting the
parties better and contrib uting to aggregate levels of polarization in the House. The same-party seat
changes do not have a significant effect in any decade, intimating that it is the cross-party sorting that has
more of an impact among Democrats. We also find that after the 1960s, redistricting does have a
significant effect on ideological change. Members who get redistricted are significantly more liberal than
members from districts that do not get redistricted. In the 1980s, Democrats in the South are significantly
more conservative, and Democrats from states with a higher GINI coefficient also become more liberal.
(INSERT TABLE 3 and 4 ABOUT HERE)
Among House Republicans, we also see that cross-party seat changes are significant. Across all
decades, seats that move from being Democrat to Republican are significantly more conservative as a
result. Thus, even among Republicans, the cross-party switching helps sort members appropriately by
party and thus clarify partisan lines in the House. The within-party changes among Republicans are less
clear. In the 1950s and 1960s, seats that switch hands but stay in the Republican party actually become
more liberal. This is consistent with our argument that partisan lines were blurred around mid-century.
Beyond electoral replacement, we find that redistricting also had an effect in the 1970s and beyond. In
these decades, Republicans from districts that had been redistricted were significantly more conservative
than Republicans from districts that had not been redistricted. Similarly, Republicans from states with a
higher GINI coefficient were more conservative. Among Republicans in the South, we see an interesting
28
result. In the 1960s, 1970s, and 1990s, Republicans in the South have a negative coefficient. This is true
even though the mean DW-Nominate score for Southern Republicans in the South is consistently more
conservative than Republicans from other regions throughout this time period. How can we interpret this
coefficient? Although Republicans in the South are more conservative than other members of the party,
they simply did not move ideologically as much as their counterparts in other regions. Thus, although
their raw DW-Nominate scores are more conservative than members from other regions, their ideological
movement is smaller, thus leading to the negative coefficient.
In the Senate, the results are largely the same as the House. Like the House, the effect of electoral
replacement is greater than the effect of other variables. Seats that go from Republican to Democrat
become significantly more liberal, while seats that go from Democrat to Republican become significantly
more conservative. In addition, in the 1960s, the key decade of change, Democrats replacing other
Democrats are significantly more liberal. Among Republicans, the seats that switch hands within the
Republican party are more liberal in the 1950s, 1960s, and 1970s. This is likely due to the influx of
northern Republicans that were pulling the party in a more moderate direction. The magnitude of that
coefficient, however, is much smaller than the magnitude of change among seats that went DemocratRepublican. Among Democrats, the number of terms served is significant in the 1970s, 1980s, and
1990s, but the magnitude of the effect is zero.
In sum, our test of the delayed replacement hypothesis against alternate explanations for the
sources of partisan polarization confirms that electoral replacement is a key part of the re-polarization of
Congress. The importance of electoral change, however, becomes clear only in light of the historic
decline in House polarization after WWII, and the subsequent delay in re-polarization at the House level.
Since most scholars have begun with the question of why the House polarized in the 1970s and 1980s,
they have been searching for sources of change in the 1970s. In truth, however, a substantial portion of
change in member ideology is explained by simple patterns of electoral replacement. By understanding
the unusually high levels of bi-partisanship around mid-century, however, it becomes clear much of the
re-polarization of the House in the 1970s and 1980s was a result of a re-sorting of parties through
29
electoral change. Other explanations, including redistricting, the changing South, income inequality, and
endogenous institutional change, are clearly also part of the story, but the entire historical story only
becomes clear by understanding the role of the personal vote and delayed electoral replacement.
Conclusion
Throughout this paper, we have argued that the polarization of the 1970s and 1980s is best
understood as a readjustment to historical norms of polarized parties. It is only in juxtaposition to the
unusual period of bi-partisanship during the 1950s that the re-polarization of the latter decades of the
twentieth century appears unusual. Thus, to understand congressional polarization in the twentieth
century, we need an explanation that takes into account the striking decline in partisanship immediately
after WWII, and the delayed return to partisanship in the House in the 1970s and 1980s. As the bipartisan issues of the 1950s gave way to the polarizing issues of the 1960s, why did the House and the
Senate lag behind the electorate and presidential elections in re-polarizing?
We argue that the personal vote played a crucial role in insulating members of Congress from
national partisan changes, by allowing members who were cross-pressured between their parties and their
districts to remain in office despite the district-party divergence. Indeed, we find that Representatives and
Senators who had been in office the longest were the most resistant to the changing partisan tides of the
1960s. It is only when these members retire or are defeated that we see polarization re-emerge. Thus,
even though presidential elections and the electorate repolarized in the 1960s, the aggregate effects of
change were not apparent in Congress until the late 1970s or early 1980s.
This paper thus makes two important refinements to existing approaches to understanding
partisan polarization in the House. First, it puts the rising polarization of the late 1970s and 1980s into its
proper historical context, thus demonstrating that an understanding of the immediate post-WWII period is
crucial to understanding the readjustment to polarization in later decades. Second, taking this historical
context into account, it demonstrates the role that the personal vote played in insulating members of the
House from re-polarizing trends in the 1960s, and the subsequent role of delayed electoral replacement in
30
reviving aggregate levels of House polarization. This historical approach thus clarifies the unusual period
of bi-partisanship in the 1950s in light of partisan convergence on key national issues, and the delayed
response of Congress to exogenous changes to the constituency bases of the party is better understood in
light of the personal vote.
In short, the historical approach to understanding increased polarization deserves to be included in
any theory of polarization. Importantly, this approach highlights the importance of taking a longer
historical view: instead of viewing the 1970s rise in Congressional polarization as an aberration, we
should instead start with the 1950s, and examine why Congressional parties did not re-polarize until the
1970s and 1980s. Starting with this question, then, it becomes clear that the personal vote and patterns of
electoral replacement play a critical role in bringing previously misaligned members of Congress back
into alignment with their parties and their districts.
31
Appendix I:
Items Included in the Issue Indexes
NOTE: In each index, the term “liberal” refers to a +1 code and “conservative” is –1.
1948
1952
1956
Role of Government
Defense
Role of Government
Race
Role of Government
Race
Defense
1960
Role of Government
Race
1964
Defense
Role of Government
Race
1968
Defense
Role of Government
Race
Defense
1972
Role of Government
Race
Rent control
US give in to agree with Russia
Involvement of government in social welfare
Government involvement in negro employment
Government should guarantee work
Government should subsidize medical care
Role of government in housing and utilities
Government involvement in negro employment and housing
Government involvement in school desegregation
Should US be tougher on communism
Military in anticommunist nations
Firing suspected communists
Aid to countries not anticommunist
Government should let private business handle housing and
utilities
Government should guarantee jobs
Government should subsidize medical care
Government involvement in negro employment and housing
Government should help integrate schools
Send soldiers to fight communists
Government subsidize medical care
Government guarantee jobs
Government guarantee fair employment
Government guarantee school integration
Is civil rights movement going to fast
Discuss differences with communists
Government aid for medical care
Government guarantee jobs
Government guarantee fair employment
Government facilitate integration
Government integrate public accommodations
Is civil rights movement going to fast
Talk with leaders of Communist countries
Trade with Communists
Government guarantee jobs and living standard: pre-election
Government health insurance scale
Government guarantee jobs and living standard: post-election
Government guarantee fair employment
Government facilitate integration
Government integrate public accommodations
Is civil rights movement going to fast
Busing to achieve integration scale
Government aid to minority groups
32
keep/extend it
give in
more government
more government
yes
yes
more help
more government
more involvement
easier
less military
fire less
more aid
no
yes
yes
more government
yes
less military
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
yes
yes
yes
no
yes
yes
Defense
1976
Role of Government
Race
1980
Defense
Role of Government
Race
Defense
1984
Role of Government
Race
Defense
1988
Role of Government
Race
Defense
1992
Role of Government
Trade with Communists
Defense spending
Government guarantee jobs and living standard: pre-election
Government health insurance scale
Government guarantee jobs and living standard: post-election
Government facilitate integration
Is civil rights movement going to fast
Government aid to minority groups
Defense spending
Government role in reducing inflation/unemployment
Government role in guaranteeing jobs and standard of living
Government role in aiding minorities
Is civil rights movement going to fast
Busing to achieve integration scale
Defense spending
Try to get along with Russia scale
Government services and spending: pre-election
Government role in guaranteeing jobs and standard of living:
pre-election
Government services and spending: post-election
Government role in guaranteeing jobs and standard of living:
post-election
Government funded medical insurance
Government role in aiding minorities
Is civil rights movement going to fast
Busing to achieve integration scale
Defense spending
Cooperate with Russia scale
Government services and spending
Government funded medical insurance
Government role in guaranteeing jobs and standard of living
Government spending on social security
Government spending on food stamps
Government spending on unemployment assistance
Government role in improving soc/econ status of blacks
Government role in improving soc/econ status of minorities
Government spending on programs to assist blacks
Is civil rights movement going to fast
Preference for blacks in hiring and promotion
Should federal government see that blacks get fair treatment in
employment
yes
less
yes
yes
yes
yes
no
more
less
more government
more government
more government
no
yes
less
yes
more
Quotas in school admission
Defense spending
Cooperate with Russia scale
Strong military v. negotiating
Do everything we can to prevent spread of communism
Government services and spending
Government role in guaranteeing jobs and standard of living
Government spending on food stamps
pro
less
yes
negotiating
no
more
more help
more
33
more help
more government
more help
more help
more
no
yes
less
yes
more
more help
more government
more
more
more
more
more
more
no
yes
yes
Race
Defense
1996
Role of Government
Race
2000
Defense
Role of Government
Race
Defense
Government spending on welfare
Government spending on social security
Government spending on unemployment assistance
Government spending on aid to poor people
Government role in improving soc/econ status of blacks
Government spending on programs to assist blacks
Is civil rights movement going to fast
Preference for blacks in hiring and promotion
Should federal government see that blacks get fair treatment in
employment
Should US maintain military power with more defense
spending
Defense spending
Government health insurance
Government responsibility to reduce gap between rich and
poor
Government role in guaranteeing jobs and standard of living
Government services and spending
Government spending on aid to poor people
Government spending on food stamps
Government spending on social security
Government spending on welfare
Affirmative action in hiring and promotion
Government aid to blacks: pre-election
Government aid to blacks: post-election
Should federal government see that blacks get fair treatment in
employment
Defense spending
Government role in guaranteeing jobs and standard of living
Government services and spending
Increase/decrease spending on welfare
Government spending on aid to poor people
Government spending on food stamps
Government spending on social security
Affirmative Action
Government aid to blacks
Government role in school integration
Spending on aid to blacks
Defense spending
34
more
more
more
more
more
more
no
yes
yes
no
less
more
yes
more
more
more
more
more
more
yes
more
more
yes
less
more
more
more
more
more
more
yes
more
yes
more
less
Appendix 2: Logit Regression Analysis of Vote Choice on Issue Preferences
Summary Statistics
Dependent Variable: Probability of Voting Democrat
For predicted probabilities, all issue indexes are set to -1 (conservative position).
President
House
%
Correctly
Predicted
Pseudo
RSquared
Senate
Year
%
Correctly
Predicted
Pseudo
RSquared
N
Predicted
Probabilities
1948
59.30%
0.06
268
37.70%
1952
70.10%
0.14
788
35.60%
62.50%
0.09
741
32.20%
60.9%
0.1
600
25.90%
1956
64.80%
0.09
984
7.10%
62.70%
0.07
899
18.50%
54.7%
0.08
688
11.40%
1960
97.50%
0.19
693
16.20%
65.60%
0.15
590
30.80%
62.2%
0.14
349
29.60%
1964
77.20%
0.34
982
10.70%
71.50%
0.18
818
30.50%
74.1%
0.18
674
19.80%
1968
66.60%
0.2
862
11.10%
60.00%
0.07
794
32.90%
65.2%
0.11
615
22.70%
1972
73.50%
0.27
1241
1.80%
60.40%
0.09
1060
22.30%
57.5%
0.05
602
38.60%
1976
66.30%
0.2
1222
12.40%
64.10%
0.15
1010
22.40%
64.3%
0.14
741
26.50%
1980
71.90%
0.31
769
7.80%
65.00%
0.15
768
24.10%
62.8%
0.14
529
24.30%
1984
75.50%
0.4
1241
1.50%
67.40%
0.21
1082
12.80%
68.8%
0.25
663
9.60%
1988
74.20%
0.39
1191
0.80%
67.50%
0.2
1049
9.70%
67.7%
0.21
839
9.10%
1992
75.00%
0.4
1324
3.00%
67.30%
0.17
1343
16.00%
66.3%
0.19
944
11.90%
1996
78.10%
0.48
928
3.80%
72.00%
0.31
931
7.20%
71.4%
0.33
543
7.70%
N
Predicted
Probabilities
%
Correctly
Predicted
Data not available
Pseudo
RSquared
N
Predicted
Probabilities
Data not available
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38
Figure 1: Difference in Party Medians, House and Senate, 1867-1999 (1st Dimension DW-Nominate Scores)
Figure 2: Determining Partisan Overlap in Congress
Republican
s
No Overlap
-1
Liberal
Overlap
10% Most
Liberal
Republican
-1
Liberal
+1
Conservative
+1
Conservative
40
Figure 3a: Partisan Convergence in the House, DW-Nominate Scores, 1867-1999
Democrats
Republicans
overlap1
40.00
overlap2
overlapm
25.00
overlap1
overlap2
overlapm
20.00
30.00
15.00
%
%20.00
10.00
10.00
5.00
0.00
0.00
1
8
6
7
1
8
7
3
1
8
7
9
1
8
8
5
1
8
9
1
1
8
9
7
1
9
0
3
1
9
0
9
1
9
1
5
1
9
2
1
1
9
2
7
1
9
3
3
1
9
3
9
1
9
4
5
1
9
5
1
1
9
5
7
1
9
6
3
1
9
6
9
1
9
7
5
Year
1
9
8
1
1
9
8
7
1
9
9
3
1
9
9
9
1
8
6
7
1
8
7
3
1
8
7
9
1
8
8
5
1
8
9
1
1
8
9
7
1
9
0
3
1
9
0
9
1
9
1
5
1
9
2
1
1
9
2
7
1
9
3
3
1
9
3
9
Year
41
1
9
4
5
1
9
5
1
1
9
5
7
1
9
6
3
1
9
6
9
1
9
7
5
1
9
8
1
1
9
8
7
1
9
9
3
1
9
9
9
Figure 3b: Partisan Convergence in the Senate, DW-Nominate Scores, 1867-1999
Democrats
Republicans
25.00
over50
over25
over10
20.00
20.00
15.00
15.00
0
>
N
0
>10.00
N
10.00
5.00
5.00
0.00
0.00
1
8
6
7
1
8
7
3
1
8
7
9
1
8
8
5
1
8
9
1
1
8
9
7
1
9
0
3
1
9
0
9
1
9
1
5
1
9
2
1
1
9
2
7
1
9
3
3
1
9
3
9
1
9
4
5
1
9
5
1
1
9
5
7
1
9
6
3
1
9
6
9
1
9
7
5
1
9
8
1
Year
1
9
8
7
1
9
9
3
1
9
9
9
1
8
6
7
1
8
7
3
1
8
7
9
1
8
8
5
1
8
9
1
1
8
9
7
1
9
0
3
1
9
0
9
1
9
1
5
1
9
2
1
1
9
2
7
1
9
3
3
1
9
3
9
Year
42
1
9
4
5
1
9
5
1
1
9
5
7
1
9
6
3
1
9
6
9
1
9
7
5
1
9
8
1
1
9
8
7
1
9
9
3
1
9
9
9
Figure 4: Electorate vs. Congressional Party Polarization, 1952-2000
Issues Related to Defense, Race, and Role of Gov’t
Race Issues
.6
.6
.5
.5
Mean Difference between Parties
Mean Difference between Parties
Defense Issues
.4
.3
.2
.1
0.0
Electorate (NES)
-.1
.3
.2
.1
0.0
Electorate (NES)
Congress (DW-Nom)
-.1
1952
1960
1968
1976
1984
1992
1964 of 1972
1988
Role
Govt.1980
Issues
1956
.6
Mean Difference between Parties
.4
2000
Congress (DW-Nom)
1952
1996
1960
1956
YEAR
1968
1964
1976
1972
1984
1980
1992
1988
2000
1996
YEAR
.5
.4
.3
.2
Electorate (NES)
.1
Congress (DW-Nom)
1952
1960
1956
1968
1964
1976
1972
1984
1980
1992
43
1988
2000
1996
NOTE: To put the issue indexes and DW-Nominate
scores on the same scale, we performed a simple
monotonic transformation of the DW-Nominate
scores, subtracting 0.4 from the mean differences of
the parties.
Figure 5: Predicted Probabilities from Logit Regression Analysis of Vote Choice on Issue Preferences
Dependent Variable: Probability of Voting Democrat
For predicted probabilities, all issue indexes are set to -1 (conservative position).
44
Table 1: The Implications of being Cross-Pressured, House
Cross-Pressured Representatives*
Democrats
Non-South
Republicans
South
All States
Not CrossPressured
CrossPressured
Not CrossPressured
CrossPressured
Not CrossPressured
CrossPressured
Mean
-0.42
-0.30
-0.10
-0.03
0.34
0.26
(N)
(3250)
(1675)
(1417)
(973)
(4650)
(891)
Ideology
DW-Nominate
Score
"Balancing"
House Vote Margin
Slurge
Voting with the Opposite
Party
10% Overlap Voting
Mean
71%
64%
88%
79%
65%
62%
(N)
(2920)
(1488)
(1278)
(861)
(4042)
(806)
Mean
6.6%
7.4%
5.2%
7.3%
6.4%
6.8%
(N)
(2920)
(1488)
(1278)
(861)
(4042)
(806)
%
0%
2%
23%
31%
8%
20%
(N)
(16)
(38)
(332)
(298)
(357)
(175)
* Defined as Democrats who are from conservative districts (districts that vote less than 45% Democratic at the presidential level) and
Republicans who are from liberal districts (districts that vote more than 55% Democratic at the presidential level)
45
Table 2: The Implications of being Cross-Pressured, Senate
Cross-Pressured Senators*
Democrats
Non-South
Republicans
South
All States
Not
CrossPressured
CrossPressured
Not
CrossPressured
CrossPressured
Not
CrossPressured
CrossPressured
Mean
-0.34
-0.20
-0.07
-0.04
0.29
0.05
(N)
(861)
(79)
(212)
(11)
(712)
(164)
Mean
60%
60%
65%
64%
58%
56%
(N)
(742)
(71)
(186)
(11)
(618)
(139)
Mean
5.7%
6.8%
3.1%
9.2%
4.9%
6.1%
(N)
(742)
(71)
(186)
(11)
(618)
(139)
%
14%
24%
48%
73%
15%
50%
(N)
(118)
(19)
(101)
(8)
(110)
(82)
Ideology
DW-Nominate Score
"Balancing"
House Vote Margin
Slurge
Voting with the Opposite
Party
10% Overlap Voting
* Defined as Democrats who are from conservative states (states that vote less than 45% Democratic at the presidential level)
and Republicans who are from liberal states (states that vote more than 55% Democratic at the presidential level)
46
Figure 6: Who Loses and Who Replaces Them? The Replacement Hypothesis
D-R
3.00
R-D
A
2.00
1.00
0.00
A
AAA
A A
A
A
A A
AA A A
A
A
A
A
A
A
A
A A
A
A A A
AA A
A
A
A
A A
A
AA
AA A A
AAA
A
AA
A
A A
A
A
A
A
A A
A
A A A
A
A
AA A
A
A
A
A
A
AA
A
A
A
A
A
A
A
-1.00
A
-2.00
-3.00
-3.00
-2.00
-1.00
0.00
1.00
Democrats who are too liberal for their
districts (residual score < 0) are replaced
by members who are more conservative
and within 1.5 s.d. of the district
preference. For example, Jim Jones (Dem)
of OK is replaced in 1984 by James Inhofe
(Rep).
47
2.00
3.00 -3.00
-2.00
-1.00
0.00
A
AA
A
A A
A
AA
A
AA
A
A
A A
A
A
A
A
A
AA
AAAA A
A
A
A
A
AA A A A
A A
A
A
A
A
1.00
2.00
3.00
Republicans who are too conservative
for their districts (residual score >0)
are replaced by members who are
more liberal and within 1.5 s.d. of
district preferences. For example,
Silvio Conte (Rep) of MA is replaced in
1990 by John Olver (Dem).
Figure 7: Change in DW-Nominate Residuals: House of Representatives
50s D-R
3.00
2.00
Residual score of replacement
1.00
0.00
-1.00
-2.00
A
AA
A
AA
A
A
AA A
A
A
A
60s D-R
A
A
A
A
A
A AA
A
AA
A
A
A A
A
AA A
AA
A
A
A
A A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA
AA
A
A
A
A
A
A
A AA
A
AA A
AA A
A
A
A
AA
AA
70s D-R
A
A
A
A
A
A
A
A
A
A
A
AA
A
A
A
AA
AA
A
A
A
A
A
AA A
A
AA
A A
A
A
AA
A
A
A
A
80s
D-R
A
A
A
A A
A
A
AA
A AA
AA
A AA
A
A
A
AA
AA
A
A A A
A
A
A
A
A
A
A
AA
A
AA
A
A
A
A
A
A
AA
A
A
AAAA
A A
90s D-R
A
A AA
A
A
AA A
A
A
AA
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA
A
A
A
A
A
A
A
AA
A
AA
A
A
A
A
A
AA
AA
A
A
AA
A
AA A A
A
-3.00
50s R-D
3.00
60s R-D
2.00
A
0.00
-2.00
80s R-D
90s R-D
A
1.00
-1.00
70s R-D
A
A
A A
A
A
A
A
A
A
A
A
A
A
AA
A
A
A AA
A
AA
AA
A
A
A
A
A
A
A
A
AA
A
AA
A
A
A
A
A
A
A
A
A
A
AAA
A
A
A
A AAAA
A
A
A
AA
A
A
A
A
A
A A
A
A A
AA
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA A
AA
AA
A
A
A
A
A
A
AA A
A
A
A
A
A
A
AA
A
A
A
A
AA
AA A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA
A
A
A
A
A
A
AA
A
A
A
A AAA
A
A
A
A
AA
A
A
A
AA
AA
A
A
A
A
A
A
A
A
A
AAA
A
A A
A
A
AA
A
A
A
A
A A
A
A
AA
A
AAA
AA
AA
A
AA
A
AA
A A
A
A
A
A
A
AA
A
AA
AAA A
A
A
A
A
A
A
AA
AA
A
A
AAA
A
A
AAA
A
A
A
A
A
A
A
A
A
A
A
AA A A
-3.00
-3.00 -1.00
1.00
3.00 -3.00 -1.00
1.00
3.00 -3.00 -1.00
1.00
3.00 -3.00 -1.00
1.00
3.00 -3.00 -1.00
1.00
3.00
-2.00 0.00
2.00
-2.00 0.00
2.00
-2.00 0.00
2.00
-2.00 0.00
2.00
-2.00 0.00
2.00
Residual Score of member out-of-office
48
Figure 8: Change in DW-Nominate Residuals: Senate
50s D-R
3.0
60s D-R
A
A
2.0
A
A
1.0
A
A
Residual score of replacement
0.0
-1.0
A
A
A
AA
A
AA
A
70s D-R
AA
A
A
A
A
A A
AA
AA AAA A
A
A A A A
80s D-R
90s D-R
A
A
A AA
A
AA A
A
A
AA
A
A AA
AA
A
-2.0
-3.0
3.0
50s R-D
60s R-D
70s R-D
80s R-D
90s R-D
2.0
1.0
0.0
-1.0
-2.0
A
A
A
A
A
A A
AA
A A A A
AA A
-3.0
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
A
A
A
A
A A
A
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
A
A
A AA
A
A AA
A A A
AA
A
AA
A
A
A
A
A
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
Residual Score of member out-of-office
49
A
A
AA
A
A
AA
A
AA
AA
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
A
A
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
Table 3: Regression of Change in Member Ideology on Electoral Replacement Variables, House
Dependent Variable: Change in 1st Dimension DW-Nominate Score
50s
B
60s
Std. Error
B
70s
Std. Error
B
80s
Std. Error
B
90s
Std. Error
B
Std. Error
DEMOCRATS
(Constant)
0.16
-0.35
Change in Constituency Preference^
0.16
-0.07
*
0.09
-0.07
0.05
-0.02
*
0.09
-0.09
0.19
-0.06
0.01
-0.02
-0.07
-0.04
**
0.05
-0.08
0.59
-0.05
# of Congresses Served
0
0
0
0
0
0
0
0
0
0
Percent Black in State
0
0
0
0
0
0
0
0
0
0
Income Inequality (GINI Coef.)
***
-0.02
-0.03
-0.25
-0.19
-0.27
-0.26
-0.5
-0.15
***
-0.07
-0.19
South
0
-0.02
0.02
-0.01
0.01
-0.01
0.02
-0.01
**
0
-0.01
Redistricting
0
-0.02
-0.03
-0.01
***
-0.04
-0.01
***
-0.03
-0.01
***
-0.04
-0.01
***
R-D Seat Changes
-0.62
-0.01
-0.62
-0.01
***
-0.51
-0.01
***
-0.56
-0.01
***
-0.66
-0.02
***
D-D Seat Changes
-0.04
-0.02
-0.01
-0.01
-0.01
-0.01
0.01
-0.01
0.03
-0.02
***
Adjusted R-Squared
0.81
0.66
0.54
0.59
0.6
N
524
1247
1334
1225
910
REPUBLICANS
(Constant)
0.16
-0.46
-0.13
-0.1
-0.33
-0.13
Change in Constituency Preference^
-0.05
-0.08
0.03
-0.03
0
-0.04
**
-0.08
-0.18
-0.09
*
0.02
-0.05
0.59
-0.09
***
# of Congresses Served
0
0
0
0
*
0
0
Percent Black in State
0
0
0
0
*
0
0
1.04
-0.36
**
0.21
-0.21
0.5
-0.22
*
*
-0.05
-0.02
**
0
-0.01
-0.03
-0.01
*
0.05
-0.01
***
0.03
-0.01
**
0.07
-0.01
***
***
0.58
-0.02
***
0.71
-0.02
***
0.06
-0.02
***
0.05
-0.02
**
Income Inequality (GINI Coef.)
-0.02
-0.05
0.47
-0.29
South
-0.01
-0.02
-0.04
-0.02
0
-0.04
0.02
-0.01
D-R Seat Changes
0.61
-0.03
***
0.56
-0.01
***
0.49
-0.02
R-R Seat Changes
-0.11
-0.01
***
-0.06
-0.02
**
-0.02
-0.02
Redistricting
**
-0.08
0
0
0
0
0
0
0
0
Adjusted R-Squared
0.66
0.68
0.49
0.63
0.71
N
358
841
801
862
779
^ Change in Constituency Preference measured as the change in the 3 year moving average of presidential vote in the district
50
**
Table 4: Regression of Change in Member Ideology on Electoral Replacement Variables, Senate
Dependent Variable: Change in 1st Dimension DW-Nominate Score
50s
B
60s
Std. Error
B
70s
Std. Error
B
80s
Std. Error
B
90s
Std. Error
B
Std. Error
DEMOCRATS
(Constant)
-0.08
-0.15
0.01
-0.07
-0.17
-0.2
-0.18
-0.13
0.25
-0.17
Change in Constituency Preference^
-0.25
-0.67
-0.11
-0.09
-0.13
-0.16
-0.12
-0.23
-0.28
-0.28
# of Congresses Served
0
Percent Black in State
0.18
Income Inequality (GINI Coef.)
0
0
0
0
-0.22
0
-0.05
-0.17
-0.11
-0.02
-0.21
0.39
0
-0.01
0
-0.33
-0.01
***
-0.25
-0.01
-0.06
-0.02
**
0.02
-0.04
0
South
-0.02
-0.05
R-D Seat Changes
-0.33
-0.02
D-D Seat Changes
0.1
-0.11
***
0
0
*
0
0
*
0
0
0.11
-0.1
-0.06
-0.16
-0.56
0.35
-0.34
-0.69
-0.41
-0.03
-0.04
-0.02
0.02
-0.03
-0.25
-0.01
-0.48
-0.03
0.04
-0.03
0.02
-0.04
***
***
Adjusted R-Squared
0.72
0.75
0.56
0.65
0.72
N
111
310
289
248
108
*
***
REPUBLICANS
(Constant)
0.01
-0.05
-0.18
-0.16
0.32
-0.19
Change in Constituency Preference^
-0.31
-0.33
-0.27
-0.2
0.71
-0.2
# of Congresses Served
0
Percent Black in State
-0.01
Income Inequality (GINI Coef.)
0
0
0
0
-0.18
-0.45
-0.15
0
0.56
-0.46
0
**
South
***
0
0
-0.11
-0.01
-0.2
0.21
-0.26
0.15
-0.35
0
0
-0.11
-0.07
-0.1
-0.31
-0.19
-0.89
-0.54
0.07
-0.29
0.13
-0.48
0.03
-0.04
0
-0.02
0.1
-0.04
*
0.85
-0.06
***
-0.02
-0.02
0.52
-0.03
***
0.59
-0.03
***
0.59
-0.02
***
0.6
-0.02
R-R Seat Changes
-0.12
-0.02
***
-0.11
-0.02
***
-0.09
-0.02
***
0.01
-0.01
N
***
0.82
0.71
0.79
0.78
0.75
80
181
201
248
85
^ Change in Constituency Preference measured as the change in the 3 year moving average of presidential vote in the state
51
0
-0.18
D-R Seat Changes
Adjusted R-Squared
0