Elite-level Issue Dynamics: Assessing Perspectives
on Issue Polarization∗
Daniel J. Lee†
Rachel A. Schutte‡
Abstract
We analyze elite-level issue dynamics of “culture war” issues in the U.S. since the 1970s to assess the
extent to which they have transformed American party politics. Previous works on issue dynamics, which
focus on changing levels in partisanship or polarization, at times confuse between three theories of issue
change — issue evolution, conflict extension, and ideological polarization. We argue that these theories
differ on a second aspect of issue conflict: dimensionality — that is, the relationship between political conflict on the issue in question and conflict on other issues. Our paper clarifies the similarities and differences
across these perspectives. We analyze changes in the dimensionality of voting in the U.S. House on the
environment, women’s rights, gun control, abortion, and immigration to present a more comprehensive
view of issue dynamics, while assessing the different perspectives of issue change. Our results suggest
that these perspectives need further clarification and development, such as the consideration of degrees of
an evolution. For many of these issues, issue conflict was simply absorbed by existing partisan cleavages,
which is a testament to the durability of the American two-party system.
∗ Work
in progress. Please do not cite without author permission.
Professor of Political Science. Michigan State University. [email protected]
‡ Ph.D. Candidate. Department of Political Science. Michigan State University. [email protected]
† Assistant
One of the most significant changes in American politics since the 1970s is the increased polarization of political elites. Poole and Rosenthal (2007) and Theriault (2008) analyze the divergence on a main
liberal-conservative ideological dimension (see also Hetherington, 2009). Other researchers have looked
within this broad ideological trend by studying polarization on individual issues, such as Civil Rights
(Carmines and Stimson, 1989), women’s rights (Wolbrecht, 2000, 2002), the environment (Lindaman and
Haider-Markel, 2002), gun control (Lindaman and Haider-Markel, 2002), and abortion (Adams, 1997). Some
observers describe the increased polarization on new issues as signaling the rise of a “culture war,” which
stresses the increased salience of moral values, relative to traditional economic values (e.g., Hunter, 1991;
Frank, 2004).
In this paper, we clarify the nature of elite (members of Congress) polarization on specific issues in
order to better understand issue dynamics. That is, we aim to develop a more comprehensive picture of
how political conflict on polarizing issues changes over time. To accomplish this goal, we analyze how
changes in issue polarization correspond with changes in the dimensionality of conflict on that issue. Previous works provide an incomplete picture of issue change because they only track changes in the degree
of polarization or partisanship on the issue — the difference in preferences (roll call voting) on an issue
between the average Democrat and the average Republican. We argue that a measure of polarization only
illustrates one aspect of issue change. Our paper places the polarization on a particular issue into perspective by observing how conflict on that issue changes in relation to conflict on other issues. Is issue change
due to changes in the broader political environment or something peculiar about a specific policy area?
And is polarization a sign of a culture war, or are these new issue conflicts simply a reflection of traditional
partisan conflict?
Our analysis of issue dynamics highlights the durability of American two-party system. The rise of
culture war issues had the potential to disrupt the major parties, either by instigating sizeable shifts each
party’s coalition or by introducing an issue space for a successful third party. But as a casual observer of
American politics knows, an increased importance of environmental issues, for instance, did not lead to
the triumphant rise of the Green Party as a viable challenger to the two major parties. We instead show
that many culture war issues have been absorbed by the existing party system, although there were some
notable differences across issues.
1
1
Theories of issue change
By focusing on changes in issue dimensionality, we highlight similarities and differences between various
theoretical perspectives of issue change: issue evolution (Carmines and Stimson, 1989), ideological polarization (Poole and Rosenthal, 2007), and conflict extension (Layman and Carsey, 2002).1
The purpose of this paper is both theoretical and empirical. We first clarify the theoretical connections,
both similarities and differences, across these three perspectives of issue change. Our discussion in particular suggests the need for clarification on the empirical research regarding issue evolution. We analyze
roll-call voting in the U.S. House on four issues that have been argued in the literature to be examples of an
issue evolution: the environment (Shipan and Lowry, 2001; Lindaman and Haider-Markel, 2002), gun control (Lindaman and Haider-Markel, 2002), abortion (Adams, 1997), and women’s rights (Wolbrecht, 2002).
These works already demonstrate elite polarization on each of these issues. We extend their findings by observing how polarization tracks with changes in dimensionality, while also considering the more recently
salient issue of immigration.
Assessing changes in dimensionality to clarify and highlight the distinctions between these perspectives is important. For instance, the consequences of polarization according to issue evolution versus ideological polarization are quite different. What we call the “strong version” of issue evolution leads to a
transformation of party conflict. Rather than reinforce the status quo, a cross-cutting issue rotates politics onto a new axis, such as racial politics during the Civil Rights era (the original example of an issue
evolution, Carmines and Stimson 1986, 1989) or values/morality during the intensification of conflict over
abortion policy during the 1990s. The polarization literature, on the contrary, claims that politics falls onto a
structured liberal-conservative continuum with Democrats more liberal than Republicans, and more issues
have become ideologically contentious over the past few decades. McCarty, Poole, and Rosenthal highlight
the difference between these two perspectives in writing, “For Carmines and Stimson [issue evolution],
American politics has become the politics of race. We are suggesting that racial politics has become more
like the rest of politics” (McCarty, Poole and Rosenthal, 2006, 52).2
1 Some of these works study elite polarization within a larger framework (e.g., Carmines and Stimson, 1989; Layman and Carsey,
2002). That is, they consider the consequences of elite polarization by analyzing the elite-mass linkage to assess issue change at the
mass public level. Our paper is not concerned with this linkage. We are only interested in clarifying the nature of elite polarization—
e.g., the first step of an issue evolution. Since elites frame issue conflict for the mass public (Carmines and Stimson, 1989; Hetherington,
2001; Layman and Carsey, 2002; Levendusky, 2009), clarifying issue change at the elite-level is an important first step needed before
one can turn to further analyzing the intricacies of the mass-elite linkage and issue change among the mass public.
2 To further see the significant difference, increased polarization on the existing cleavage likely decreases the likelihood of a strong
evolution — it is difficult for new issues to rise in salience when debate on current issues is so contentious. If partisan conflict is
high and parties are starkly differentiated on some ideological dimension, then political elites would have difficulty raising a new
cross-cutting issue to change the terms of debate, since there is already so much at stake under the status quo.
2
Our empirical analysis suggests that considering degrees of an issue evolution is beneficial. That
is, rather than treat issue evolution as a “yes or no” concept, we find that some issues show more or less
evidence consistent with an evolution. By appreciating the subtle differences across issues, we can order
the issues in terms of the strength/significance of an evolution.
We also reconcile contradictory accounts of issue conflict since the 1970s. Some observers stress the
increased presence of a culture war, which has introduced newly divisive rhetoric into the political debate, challenging traditional, economic political arguments and old lines of division. Meanwhile, other
researchers instead note the increasing partisanship and concurrent drop in the influence of cross-cutting
cultural divisions (i.e., race issues) during that same time period. We show how both accounts are to some
extent true.
1.1
Strong issue evolution
Two versions of issue evolution have been asserted in the literature. The first, which we refer to as the
strong version, is closely intertwined with the concept of realignment, as it makes specific claims on the
nature of partisan change: the new issue is cross-cutting and changes the terms of political debate, altering
the partisan cleavage (e.g., Carmines and Stimson, 1989; Carmines and Wagner, 2006). The second, which
we refer to as the weak version, does not require any realigning element to the new issue and instead only
focuses on the elite-public linkage: elites polarize on an issue, and the mass public follow elite cues to
similarly polarize or sort. This less stringent view is what researchers currently often mean when alluding
to the issue evolution perspective (see especially Stimson, 2004).
In many published works, proponents of the issue evolution perspective make a very specific claim on
the nature of partisan change. They (e.g., Carmines and Stimson, 1986, 1989; Carmines, 1991; Carmines and
Wagner, 2006) assert that the issue instigates a realignment (although they also critique realignment theory,
which we discuss further below). At the heart of the theory is the introduction of a cross-cutting issue that
alters the existing partisan cleavage. Stressing the notion party realignment, Carmines and Stimson write:
But occasionally issues rise from partisan obscurity and become so contentious, so partisan,
and so long lasting that they come to define the party system in which they arise, to transform
the grounds of debate which were their origin. This joint transformation of issues and party
systems, which we call issue evolution, is realignment in the ordinary English usage of that
term. [emphasis added] (Carmines and Stimson, 1986, 901)3
3 Carmines
and Stimson define realignment elsewhere as simply “the transformation of an existing alignment caused by the intro-
3
Carmines states elsewhere that:
[Issue evolutions] do not reinforce the existing party alignment. Instead, they cut across the direct
line of evolutionary development. They emerge from the old environment, but once having
emerged they introduce fundamental tensions into the party system and are inconsistent with the
continued stability of old patterns. [emphasis added] (Carmines, 1991, 74)
In an application of the issue evolution perspective, Adams writes:
An issue evolution can produce the same result as a realignment, but the process unfolds over a
longer period of time. . . Under the theory of issue evolution, a few rare issues exist with the capacity to instill fundamental and permanent changes in the party system. [emphasis added] (Adams,
1997, 719)
Importantly, the issue must leave “an indelible imprint” on the party system (Carmines and Stimson,
1989, 13), whereby the new issue displaces (transforms) the previously dominant dimension of conflict.
This perspective is consistent with the traditional view of partisan realignment (see Key, 1955; Sundquist,
1983; Aldrich, 1983; Miller and Schofield, 2003), and it has used a similar framework and language as the
realignment literature. The introduction or a new issue, such as race, by strategic political elites can induce
such a realignment, which can take several years and elections to occur.4
Recent research on the rise of “culture wars” is also related to this stronger form of issue evolution.
Especially since the 1980s and 1990s, so the argument goes, cultural, social and moral issues increasingly
divide the public and politicians, rather than simply questions over the economy (for a review, see Fiorina, Abrams and Pope, 2005). Some researchers argue that traditional economic conflict has been in part
replaced by a post-materialist dimension (Inglehart, 1981; Inglehart and Abramson, 1999).
Previous research does not appropriately assess such changes to partisan cleavages and instead only
base evidence on comparisons of voting scores (e.g., party unity) on a particular issue over time. Increased
intra-party consistency and inter-party difference are taken as evidence of the first step of an issue evolution
(the second step being mass public response). Showing an increase in partisan differences on an issue,
however, falls short of conclusively showing a strong issue evolution. That is, one cannot observe, for
example, whether an evolution has occurred on abortion by simply observing votes on abortion. One
duction of a new dimension of conflict” (Carmines, 1994, 77; Carmines and Wagner, 2006, 69).
4 The difference between issue evolution and traditional realignment theory that proponents have noted is that the former is a
gradual process, while the latter often posits sharp change from a critical election (e.g., Key, 1955; Burnham, 1970).
4
needs to also assess how voting on abortion changes in relation to voting on other issues, in particular
issues related to the party cleavage that dominated before the conjectured evolution.
To be clear and fair, even the strong issue evolution perspective does not necessarily call for a complete displacement of the originally dominant dimension. Carmines and Stimson (1989) give considerable
thought to the similarities between issue evolution and realignment (see also Carmines and Wagner, 2006),
and they note that issue evolution is “a considerably more subtle phenomenon” compared to the realignments during the Civil War and the New Deal (Carmines and Stimson, 1989, 20). Our theoretical discussion
and empirical analysis suggests that this perspective may benefit from a more clear and explicit description
of the characteristics of this subtle phenomenon (with a more precise description of how it differs from
realignment). Our clarification and empirical analysis aids in determining degrees of an issue evolution.
1.2
Weak issue evolution
The second version of issue evolution, which we refer to as the weak version, does not require the new
issue to realign political conflict (i.e., displace or alter the old partisan cleavage).5 This view is what some
researchers now mean when thinking of the issue evolution perspective, which Stimson (2004) and numerous applications (e.g., Adams, 1997; Wolbrecht, 2000) of issue evolution adhere to — albeit at times
inconsistently, which we point out below.
We find only one instance (to our knowledge) of the issue evolution perspective explicitly theorizing
a weaker version of issue change. Stimson writes in his updated discussion of the topic:
We know that a two-party system tends to create a single issue division that is stable over time,
that it generates new issues as a predictable response to the needs of otherwise losing parties
to shake up the system, and that these new issues gradually become incorporated into the old issue
configuration with the passage of time. [emphasis added] (Stimson, 2004, 69)
This formulation is somewhat different from earlier work by de-emphasizing the realigning nature of evolutions — and it is telling that Stimson characterizes issue evolution as issue alignment, rather than realignment, in this more recent book.
Although applications of the issue evolution perspective show evidence in support of the weak version, they still have tended to use the language of the strong version. One can see this in the Adams (1997)
5 We do not mean to use the term “weak” in any negative sense. We use the terms strong and weak to only point out that the strong
version adds the requirement on changes in dimensionality (realignment) that imply a more significant change to partisan conflict
from an evolution. The weak version does not require any such change to the party system and instead argues that new issues,
although originally cross-cutting, will align onto pre-existing partisan cleavages as the issue evolves.
5
quote above. Wolbrecht (2000) also conflates the two versions in her analysis of women’s rights. Wolbrecht
(2000, 4) in parts supports the strong version, at one point contending, “polarization over women’s rights
has emerged as one of the most readily identifiable, if not defining, distinctions between the parties” (emphasis added). The theoretical discussion also draws heavily from the classical realignment literature, and
views issue evolution as directly extending that literature (Wolbrecht, 2000, 111-115). At the same time,
Wolbrecht alludes to the weak version in her theoretical discussion, which is based on the one-dimensional
Downsian model (Wolbrecht, 2000, 108-111), since any discussion of realignment (strong version) should
utilize a multi-dimensional model. This one-dimensional focus then contributes to her empirical approach
in supporting the weak version in arguing that elites instigated an evolution when “[w]omen’s rights issues
took on a sharp dimensionality, mapping onto the left-right political spectrum” (Wolbrecht, 2000, 12). Such
mixing and matching of the strong and weak versions, we argue, is problematic, since it masks potentially
distinct issue dynamics.
The difference between the strong and weak versions puts into perspective the significance of partisan
changes on individual issues. Quoted above, Wolbrecht claims that women’s rights is now perhaps the
defining distinction between the parties. The problem with this statement is that if the weak version is
correct, then one could pick nearly any issue today and claim that it is a defining distinction between the
parties, since the parties are highly polarized on nearly all issues. One would have difficulty in judging
whether women’s rights, the environment, abortion, immigration, tax policy, social security, or gun control
is better or worse at distinguishing between the parties.
The confusion between the weak and strong versions is in the usage of the term “realignment.” The
strong version, in alluding to comparisons between issue evolution and classical realignment theory, asserts that party change is a true realignment, in the sense of changing dimensions of political conflict (e.g.,
Burnham, 1970; Sundquist, 1983; Aldrich, 1983). The weak version instead talks about realignment on the
issue in question. That is, there is no assertion of how change on that issue changes its relationship to conflict
on other issues. It simply posits a re-sorting of parties on that issue.6
6 To clarify the unique quality of true realignment, suppose we have a liberal to conservative ordering of legislators on the preexisting dominant dimension. Now suppose we have a new issue, such as abortion, that comes onto the scene and is initially crosscutting. If issue positions change such that preferences on abortion match preferences on the pre-existing dominant dimension, then
a strong issue evolution did not occur, even if policy preferences on abortion polarized. The abortion issue, as it became increasingly
structured, did not leave “an indelible imprint” on the party system—preferences (ordering of legislators) on the pre-existing dominant
dimension did not change. Instead, party positions on abortion realigned to fit onto the dominant ideological dimension. This
difference between realignment instigated by a new issue versus realignment on an issue is critical.
6
1.3
Ideological polarization
The third perspective is that supposed issue evolutions were simply instances of increased issue ideological
consistency (partisan sorting) and a reflection of a general trend of polarization on the pre-existing dominant ideological dimension since the 1970s. Poole and Rosenthal (2007) and McCarty, Poole and Rosenthal
(2006) take this view, which we refer to as ideological polarization. When a new issue emerges, conflict is
not necessarily partisan. It may be unstructured and cut across partisan lines. As the issue develops, the
parties incorporate it into the existing major party cleavage — Democrats take one side and the Republicans take the other side. That is, the the competing sides on the issue sorts into the two party’s camps. The
parties polarize on these issues because the parties are polarized in general (and increasingly so since the
1970s) and not uniquely on the issue in question. McCarty, Poole and Rosenthal (2006) and Poole and Rosenthal (2007) critique the issue evolution perspective by arguing that conflict on racial issues now simply
reflects economic conflict, which is the canonical ideological dimension.7
Looking at studies that consider the consequences of elite polarization, we see similarities to the issue evolution literature. Hetherington (2001) and Levendusky (2009) consider at the implications of elite
ideological polarization, arguing that voters have become more sorted, whereby voters holding liberal (conservative) issue stances are more likely to associate themselves with the Democratic (Republican) party. The
increase in sorting is due in large part to polarization among political elites, which clarifies the party’s reputations on those issues. The elite mass-linkage, which is also a part of the conflict extension perspective
(discussed in a following section), is quite similar to the issue evolution perspective.8
To illustrate this point, Figure 1 maps the processes of voter sorting and issue evolution, which are
taken directly from Levendusky (2009, 13) and Carmines and Stimson (1989, 160). Notice that the sorting
process described by Levendusky appears to be identical to the issue evolution perspective. So on the one
hand, issue evolution and partisan sorting are essentially the same by stressing how polarization among
elites clarifies issue differences, which is then reflected by changes in the public. On the other hand, there
is a significant difference between strong issue evolution (Figure 1.B, Carmines and Stimson, 1989) and the
other perspectives on party issue dynamics (Figure 1.A, Levendusky, 2009).9 The difference is that in a
strong issue evolution, the polarizing issue is some new cross-cutting issue that alters the partisan cleavage
7 See also Abramowitz (1994), who questions the evidence of Carmines and Stimson (1986, 1989) on similar grounds of ignoring the
relationship of conflict on racial issues with conflict on other issues.
8 There are to be sure differences in the specific dynamics of the elite-mass connection, but since our focus is on elite-level changes,
we ignore those differences.
9 Levendusky (2009) appears to stress the consequences of general trends of elite polarization and does not give much attention to
issue-specific differences. He also gives no mention of a “cross-cutting” quality of changing issues and instead focuses on increased
ideological consistency across the issues.
7
— an added condition not explicitly stated but yet differentiates the two theories in Figure 1.A and 1.B.
[Figure 1 about here.]
1.4
Conflict extension
The fourth perspective on issue dynamics is conflict extension (Layman and Carsey, 2002; Layman et al.,
2010). Although the unidimensional argument of ideological polarization of Poole and Rosenthal (2007)
differs from the multidimensional conflict extension perspective, we take that difference to be somewhat
semantic. In both perspectives, issue displacement is not necessary for polarization on a new issue — and in
this way differs from issue evolution and other realignment perspectives (e.g., Burnham, 1970; Sundquist,
1983; Aldrich, 1983; Carmines and Stimson, 1989). Furthermore, although conflict extension is multidimensional, the parties’ positions across issues are strongly correlated. That is, if a party takes a conservative
stance on one issue, then they are conservative on another. This correlation essentially reduces the multidimensional space into a single liberal-conservative dimension that describes conflict across all issues.
Because we see a larger substantive difference between the ideological polarization and issue evolution
perspectives, we give most attention to that comparison.
1.5
Simplifying to two general perspectives
Our intention is not to simplify each perspective to minimize their unique contributions. But when focusing
on the dynamics of issue change at the elite-level, there are two primary aspects of change on which we
make comparisons. One is the increased partisan division and polarization on issues. The second is how
changes on the issue in question influences how conflict on that issue compares to conflict on other issues.
All four perspectives agree that elite polarization is evidence of issue change. The difference then lies
in the claims made on the “significance” of the new issue — does the new issue add something new to party
conflict, or does it merely reinforce pre-existing conflict? The odd perspective out in this regard is strong
issue evolution, which posits a realigning quality of new issues. The other three perspectives (weak issue
evolution, conflict extension, ideological polarization) posit that as a new issue evolves, it works its way
into the pre-existing dimension of conflict.
8
2
Assessing party change and issue polarization
Our empirical approach is to observe changes in the dimensionality of roll call voting in the U.S. House
on an issue. Different patterns will be consistent with different perspectives on issue polarization. (See
Appendix A for a spatial representation of the following discussion.) Discussing our expectations in terms
of the data that we use helps clarify our main points. Our analysis utilizes Poole and Rosenthal’s firstand second-dimension NOMINATE scores, which have the commonly accepted interpretation that the first
dimension captures government intervention in the economy and the second tends to capture regional
conflict, which during most of the recent era is understood to be civil rights (Poole and Rosenthal, 2007).
Each dimension score runs from −1 to 1 (liberal to conservative), and we interpret vote models that use a
member’s NOMINATE score to predict her roll call vote and interpret the results in the following way:
• First-dimensional: If voting on an issue is explained by existing partisan cleavages, then first-dimension
NOMINATE scores largely predict voting behavior on that issue.
• Cross-cutting cutting: Second-dimension NOMINATE scores will significantly predict voting on that
issue.
• Mixed: If the issue is somewhat cross-cutting, then scores on both dimensions are needed to predict
voting on that issue.10
Although Poole and Rosenthal (2007) have shown that overall roll call voting has become more onedimensional since the 1970s, our analysis examines differences across issues within that larger trend. If
there is a strong issue evolution, then legislator preferences on some other dimension adds independent
information to preferences on the pre-existing dominant partisan dimension of conflict (first dimension
NOMINATE). In other words, if the environment (or abortion or women’s rights) is transformative, then
conflict on that issue should not simply reproduce pre-existing partisan conflicts. It should bring to the
table something unique and new, moving beyond the first dimension NOMINATE (i.e., the cross-cutting or
mixed cases).
To further illustrate what empirical patterns are consistent with each perspective on issue polarization, Figure 2 depicts three potential patterns of correlation between legislators’ preferences on a specific
10 Some caveats apply. Is that it is possible for a cross-cutting issue not to map onto the second dimension NOMINATE, which
captures an issue dimension for issues that have many roll calls that similarly influence voting decisions of many members. Since the
issues that we are analyzing make up a small proportion of votes, this concern may be pertinent. Low predictability of voting based
on either dimension of NOMINATE scores (voting does not fit into the dimensions recovered by the NOMINATE procedure) can
also describe an issue that is cross-cutting. For space considerations, leave the analysis that considers this possibility in Appendix C.
Additionally, low classification rates using scores from either dimension is also consistent with the possibility of a mixed issue.
9
issue, like the environment (say a scale of −1 pro-environment, to 1 anti-environment), and first and second
dimension NOMINATE scores (−1 liberal, to 1 conservative) over time. In all three hypothetical scenarios,
we start the time series at a point where voting on the environment is not entirely structured along a single ideological dimension (although we suppose in our example that it is slightly more structured on the
first dimension)—voting on the new issue is not yet structured. From time 0 to time t∗ , we move through
an adjustment phase, where the parties are beginning to change voting patterns on the environment as an
attempt by strategic elites to instigate an evolution. After time t∗ , the three hypothetical situations differ.
[Figure 2 about here.]
Figures 2.A and 2.B are illustrations of potential strong issue evolutions. Figure 2.A depicts the case
where the issue (environment) becomes fully structured along the second dimension. In this case, voting
is entirely independent (orthogonal) to the pre-existing partisan cleavage — the “cross-cutting” case. In
Figure 2.B, preferences and voting on the environment are increasingly explained by the second dimension.
But in the end it remains a product of preferences on both ideological dimensions — the “mixed” case.11
This case is where a strong evolution results in only a partial displacement.12
Figure 2.C depicts the case where conflict on the environment is subsumed into the dominant ideological dimension, which is consistent with the perspectives of weak issue evolution, conflict extension, and
ideological polarization.13 After the adjustment period, preferences on the environment are increasingly
correlated with preferences measured by the first dimension of NOMINATE.
3
Analysis
We analyze changes in the dimensionality of roll call voting on the environment, gun control, abortion,
women’s rights, and immigration. We also consider immigration as a more recent issue that some view
as part of the contemporary “culture war” in American politics. Voting on tax and budget is used as
a baseline for comparison — canonical economic issues that are broadly understood to be measured by
first-dimension NOMINATE. Our analysis shows that voting on all issues is increasingly predictable by
11 See
Figure 8 in Appendix A for an alternative graphical representation of these same scenarios.
slightly amended version of Figure 2.B also depicts a possible strong issue evolution. Suppose that the dotted line (correlation
between preferences on the environment and second dimension NOMINATE) does not increase (remains flat). Even if voting on the
issue is not increasingly structured on the second dimension NOMINATE, that issue is moving beyond the first dimension (correlation
with first dimension NOMINATE decreases). As stated above, for issues that make up a small portion of votes, it may be structured
on a dimension not captured by the NOMINATE scaling procedure. This point is covered further in Appendix C.
13 This again assumes that the content of first dimension NOMINATE does not change over the observed time period. This assumption is supported by McCarty, Poole and Rosenthal (2006) and Poole and Rosenthal (2007), as well as our use of budget and taxation
votes as a baseline.
12 A
10
first-dimension NOMINATE scores over time, although the timing for each issue differs. This pattern is
shown first using aggregate-level data on the environment, then by using a vote-level analysis for all of the
issues. Our results call into question previous claims of realigning evolutions on many of these issues.
3.1
Data
Our data set of roll call voting in the U.S. House spans the 92nd to 110th Congresses (1971 to 2008), which
is the time frame of the supposed issue evolutions.14 By analyzing roll call votes, we are of course limiting
ourselves to observed conflict on issues that successfully make it onto the legislative agenda. Observing
these votes (a byproduct of whatever “agenda-setting powers” the parties may have) is not problematic
for our purposes. In fact, observing the votes that do make it to the House floor is precisely what we
should analyze to assess issue change, since part of an evolution or change on an issue can relate to agenda
control.15 To measure House member placement in a two-dimensional policy space, we use first- and
second-dimension NOMINATE scores. Data availability allows for a more in-depth analysis of voting on
the environment.16 We utilize scores from the League of Conservation Voters (LCV) to measure legislator
preferences on the environment, which vary from 0 to 100.17 The score is calculated as the percentage of
votes, which are deemed important to the LCV, that the member voted for the group’s side. Higher scores
denote a higher support for pro-environment (liberal) positions. Because our analysis does not require intertemporal comparisons of LCV scores, we simply use the raw scores rather than adjusted scores (Shipan and
Lowry, 2001).
These measures are assumed to capture preferences on a particular dimension, which influences roll
call voting behavior. LCV scores capture preferences on environmental issues, and NOMINATE scores
capture preferences on the first and second ideological dimensions. As earlier discussed, implicit in our
analysis is the assumption that there was not a significant shift in the content of the first-dimension NOMINATE during this time period, which has been substantiated in earlier work (e.g., McCarty, Poole and
14 Note
that electronic voting was instituted in the 93rd Congress.
desire to keep party-splitting issues off of the legislative agenda suggests that our results might underestimate the extent to
which issues are cross-cutting (and hence evolutions).But we believe agenda control is one tool that the parties (especially majority)
can use to shape issue conflict. That is, whether the parties take opposing views on an issue is in part a product of their strategic
choices – how salient will the parties make an issue and will it make it onto the (legislative or campaign) agenda? For instance, for
the canonical example of issue evolution (racial politics in the 1950s and 1960s), the strategic choice of pushing civil rights onto the
agenda was a major contributor to change on that issue (Carmines and Stimson, 1989). This justifies the use of roll call voting behavior
to analyzing issue dynamics in all previous work on issue change, as well as our own presented analysis. Also see some discussion of
agenda control in Appendix C.
16 The other issue areas of abortion and women’s rights lack available interest group scores. The National Right to Life Committee
(NRLC) publish scorecards for members of Congress, but this is only available since the 105th Congress.
17 Unlike for some other interest group scores, such as the Americans for Democratic Action (ADA) scores, the number of votes
included in the LCV score varies Congress to Congress. The number is roughly between 20 and 40 votes per Congress.
15 The
11
Rosenthal, 2006), as well as in our later analysis of the taxation and budget baseline.
Lastly, our vote-level analysis requires a determination of which roll-call votes deal with each policy
area. We use the Public Institutions and Public Choice (PIPC) House Roll Call Database to make these
determinations.18
3.2
First look: The Environment
Our first brush at analyzing issue change focuses on the environment, which utilizes the LCV scores. Our
first piece of evidence is to observe correlations between legislators’ LCV scores and their first- and seconddimension NOMINATE scores by Congress. The potential patterns were discussed earlier and depicted in
Figure 2. In this portion of the analysis, we flip the NOMINATE scale (multiply by −1) so that the LCV and
NOMINATE scales both run from most conservative to most liberal.
[Figure 3 about here.]
The patterns observed in Figure 3 are striking and consistent with the claim that the environmental
issue dimension has collapsed onto the dominant ideological dimension since the 1970s, which most resembles Figure 2.C. The correlation between LCV and first dimension NOMINATE scores increases over
the time series from under 0.6 to above 0.9. Conversely, the correlation between LCV and second dimension
NOMINATE scores drops from just under 0.6 to less than 0.1 over the same time period. This increase in
first-dimensionality coincides precisely with the increase in elite polarization on the environment (Shipan
and Lowry, 2001; Lindaman and Haider-Markel, 2002) and is consistent with the weak version of issue
evolution. Rather than introduce a new partisan cleavage, voting on the environment polarized as it was
subsumed into the main dimension of partisan conflict. Karol (2009) runs a similar analysis for abortion
and gun control. Rather than use interest group scores, he creates issue support scores (based on roll call
votes), which shows the same general pattern of correlations. Those issues, like the environment, appear to
have been absorbed by first-dimension NOMINATE over time.19
Looking at aggregate voting data and correlations only gives a broad overview of issue change. We
can provide more nuance in illustrating how an issue has collapsed onto the main ideological dimension by
using a vote-level analysis. The basic approach is to estimate various probit models that predict votes on a
18 Data
are available at http://www.poli.duke.edu/pipc/data.html.
choose to limit portions of our analysis to the environment by using LCV scores, since the other issues have a smaller and
more variable number of roll call votes per Congress (with some Congresses having zero votes). Scores for the other issues are likely
less accurate measures of preferences, given the small number of votes from which they are based on.
19 We
12
given issue within a Congress. The models differ in the independent variables included, and the predictive
success of each model is compared to gauge which factors (dimensions) most influence voting.20
The dependent variable is the vote, coded 1 if yea and 0 if nay. The independent variables included
are either just first-dimension NOMINATE, both first- and second-dimension NOMINATE, and for our
analysis on the environment the LCV score. To assess model fit, we compare the percent classified correctly
— i.e., the percentage of votes that are correctly predicted by the model.21 That is, for each issue, we sum
the total number of correctly predicted votes and divide by the total number of votes cast. This provides us
for each issue in a given Congress the proportion of correctly classified votes.22
This analysis allows us to determine what factors (dimensions) contribute most to voting on an issue.
As an example, suppose we are interested in comparing a model that uses first-dimension NOMINATE
scores to a model that uses LCV scores to predict votes on the environment. For each environmental roll
call vote, we estimate the equations,
pi = α0 + α1 × 1st -d NOMINATEi + ε
(1)
pi = β0 + β1 × LCVi + ε
(2)
where (1) is the one-dimensional NOMINATE model and (2) is the LCV model, pi is the probability legislator i votes yea, and ε is a normally distributed error term. Using the estimated parameters, we then predict
whether a legislator votes for or against the measure, and a vote is correctly classified if the legislator votes
how the model predicts. We do this for every environmental roll call vote during a Congress and then
aggregate, calculating the percentage of environmental votes correctly classified in that Congress. If firstdimension NOMINATE captures conflict over the environment, then we would expect classification rates
from the first NOMINATE model (1) to be equal to classification rates for the LCV model (2). If environment
is not captured by the first ideological dimension, then the LCV model will produce higher classification
rates.
20 Another possible measure of issue dimensionality is the angle of the cutting line for each roll call vote. See the Appendix for
a more in-depth discussion of cutting lines. In the two-dimensional NOMINATE space, a vote that is first-dimensional will have a
cutting line perpendicular to the x-axis (90 degrees). The more important the second dimension, the greater the deviation the cutting
angle will be from that 90 degree line (either towards 0 or 180 degrees). However, given the caveat that the cross-cutting nature of the
issues we are considering might not be captured by the second-dimension NOMINATE scores, cutting angles suffer from ignoring
that possibility. For that reason, we use vote classification.
21 An alternative measure of model fit is the proportional reduction in error (PRE) (Poole and Rosenthal, 2007; McCarty, Poole and
Rosenthal, 2006). The PRE avoids inflation of classification success from unanimous votes. Since we are interested in within-vote
comparisons, rather than over time comparisons, this concern is not problematic for our results. We use vote classification because it
is a straightforward and intuitive measure.
22 We exclude all unanimous votes from our analysis.
13
We can also measure the extent to which the issue is structured off of the first dimension by comparing
classification success of the two models,
pi = α0 + α1 × 1st -d NOMINATEi + ε
(3)
pi = β0 + β1 × 1st -d NOMINATEi + β2 × 2nd -d NOMINATEi + ε
(4)
If the issue is highly structured on the first-dimension, then (4) will not improve classification success over
(3). On the other hand, if the issue is structured off of the first dimension, then (4) will improve classification
success.23
A few patterns emerge in Figure 4. First, the classification rate trends upward for all models. Second
and more relevant to our analysis, comparing the two models that include NOMINATE scores, accounting
for a second dimension adds less over time to predicting votes (the gap in the percent correctly classified
decreases over the time span). In the 93rd Congress, including second dimension scores increases the
percent classified by around 2.7 percentage points. By the 110th Congress, the second dimension improves
the model prediction by less than one percentage point. These two observations reflect the general trend
in roll call voting over this time period (Poole and Rosenthal, 2007). And importantly, this general trend
applies specifically to votes on the environment. Contrary to the strong version of issue evolution, the
conflict on the environment is increasingly coalescing on the first dimension. A last observation is that the
model that only includes the LCV score most clearly outperforms the 1st-dimension NOMINATE model
only during a few of the early Congresses (93rd through 95th), which is the the period where preferences
on the environment is least correlated with the 1st-dimension NOMINATE and most correlated with the
2nd-dimension scores (see Figure 3). That is, preferences on the environment are increasingly reflecting
preferences on the 1st dimension, shown by the similar classification rates based on predictions using 1stdimension NOMINATE scores versus LCV scores.
[Figure 4 about here.]
A few conclusions can be drawn from this analysis. First, voting on the environment indeed fits a
spatial model of voting. Models that use NOMINATE scores to predict votes perform essentially as well
as using a more specific measure of environmental support (LCV score). Second and most central to our
discussion, the environment has collapsed nearly entirely onto the main liberal-conservative ideological
23 A caveat (also stated in an earlier footnote) is that a preferences on a cross-cutting issue may not be captured by second dimension
NOMINATE scores—classification rates may be small regardless of what scores are used. We also account for this possibility in
Appendix C.
14
dimension by the 110th Congress, which is not consistent with a strong evolution. The improvement of fit in
that Congress of the two-dimensional over the one-dimensional model (just under one percentage point) is
slightly below the improvement when looking at all non-unanimous votes (Poole and Rosenthal, 2007). The
pattern of increased one-dimensionality from the 93rd Congress based on Figures 3 and 4 is striking, and
it corresponds with increased polarization on that issue (Shipan and Lowry, 2001; Lindaman and HaiderMarkel, 2002). That is, voting on the environment polarized as roll call voting on that issue increasingly
reflected voting patterns on traditionally ideological and partisan issues (first dimension NOMINATE),
which was polarizing during that time independent of any changes in environmental politics (McCarty,
Poole and Rosenthal, 2006; Theriault, 2008).
3.3
Environment, Abortion, Gun Control, Women’s Rights, and Immigration
Previous work on issue change and issue evolution has focused on the increased partisanship in roll call
voting. Figure 5 plots for each issue area the percentage of roll call votes that are “party votes” (defined in
this figure as votes that two-thirds of Democrats vote in opposition to two-thirds of Republicans) in each
Congress for each issue. We use a slightly higher threshold (than, say, 50-50) to track more intense partisan
differences. The reader should take some of these patterns with a grain of salt, since some issues had only
only one roll call vote in a Congress — e.g., immigration in the 96th Congress (see Appendix B for the
number of roll calls per Congress for each issue). This figure largely corroborates earlier research, which
use varying issue codings. Generally speaking, voting has become increasingly partisan, especially since
the early 1980s.
[Figure 5 about here.]
To simply conclude that politics on these issues have become more partisan glosses over potentially
important differences across the issues and does not help adjudicate between the various theories of issue
change. To dig deeper into the issue dynamics to assess any differences across issue areas, we run the
vote classification analysis for each issue, which utilizes first- and second-dimension NOMINATE scores
as the predictors of roll call voting — i.e., we estimate equations (3) and (4). Figure 6 presents our results
for all four issues of purported evolutions, as well as immigration. To further highlight potential differences between these new issues and traditionally ideological and partisan issues, we present results on
economic/tax/budget votes as a baseline.
[Figure 6 about here.]
15
A couple general observations are immediately evident. Voting for all issue areas has become increasingly predictable over the time period (upward trends in Figure 5.A). Even for economic issues, classification success is lower for earlier Congresses (around 83% in the 92nd Congress), but that reflects a general
pattern of low vote predictability during that time, which has given way to higher predictability in recent
Congresses (McCarty, Poole and Rosenthal, 2006). A second observation is that all issue areas have become
increasingly one-dimensional (downward trend in Figure 5.B). As expected, economic policy is consistently
close to a first-dimensional issue — controlling for the second dimension does not add much to vote prediction, and there is little Congress-to-Congress volatility compared to the other issues. But even for that issue,
the second-dimension did contribute somewhat to voting during the earlier years. One can remember, for
instance, the support by some Democrats for Reagan’s spending and tax cuts during the 97th Congress
(1981-1982). All in all, the pattern for economic votes provides a basic baseline on which to compare the
other issues. Although there is quite a bit of variability across issues (which we delve into further below),
the general pattern is that the percent improvement from the two-dimensional model at times hovers above
the line for economic policy during the earlier periods in Figure 5.B., but they have by the last Congress in
our data set (110th Congress) converged. That is, over time, roll call voting for all the issues in our analysis
have increasingly reflected conflict over traditional economic issues, and by the 110th Congress all issues
are similarly one-dimensional (percent improvement is roughly 1.5% for all issues).
We assess changes in the percent improvement of the two-dimensional model, covering each issue
in turn in order to point out differences across the issues.24 In Appendix C, we assess changes in overall
model fit to account for the possibility that cross-cutting issues are are not necessarily captured by seconddimension NOMINATE. Due to space considerations, we leave that discussion for an appendix because of
the striking patterns we observe for the percent improvement from the two-dimensional model.
3.3.1
Environment and women’s rights
During the early Congresses, there is some evidence that the environment and women’s rights were indeed emerging as a structured cross-cutting issue. The gap between the percent classified for the oneand two-dimensional models is consistently largest for environmental issues during the earlier Congresses
(up through say the 96th Congress). Consistent with earlier accounts of the women’s rights movement,
24 One may of course like to have clear cut statistical significance tests when making such comparisons of model fit. Unfortunately,
none is available, but we believe that much can still be gathered from our analysis. Herron (1999) does provides a method to estimate
standard errors for classification rates of individual roll calls, based on the uncertainty in each member’s votes. We, however, are
aggregating roll calls within a Congress, and we are not aware of a method to recover standard errors in such a case. We are also not
aware of a likelihood ratio test that can pool across all vote models within a Congress.
16
conflict on that issue was cross-cutting soon after passage of the Equal Rights Amendment by the House
and Senate in the 92nd Congress. Figure 5 suggests that this did not really occur until the 94th Congress
(1975-1977), where the percent improvement of the two-dimensional model reaches a high point. Since that
period, however, as for the environment, the issue immediately began to fall back onto the existing partisan
cleavage as voting polarized, rather than redefine partisan politics.25
3.3.2
Abortion
Since these are indeed distinct issues that have different histories, it is not surprising that the timing of
their rise and falls appear to be different. Out of the five issues that are in our analysis, abortion and
gun control show the most stark differences.26 Voting on abortion during the period soon after Roe v.
Wade is characterized by low predictability, regardless of whether one accounts for a second dimension
(see Appendix C for more discussion on this point). Evidence of abortion as a structured cross-cutting issue
does not begin to emerge until the very end of the 1980s and the early 1990s. Its pinnacle coincides with
the Republican Revolution from the 1994 congressional elections — controlling for a second dimension
increases classification success by over eight percent in the 104th Congress. Immediately following the
104th Congress, however, abortion began to incorporate back into the first dimension, and looking at voting
in the 110th Congress, we see that abortion has been fully absorbed into the first dimension.
What is especially interesting about abortion is that the era during which abortion is systematically
a cross-cutting issue is precisely a period of a sharp increase in polarization (the 1990s). Women’s rights
and the environment, however, show a trend of decreased contribution of second-dimension NOMINATE
scores during that time. Thus, the interesting change for abortion is not simply that roll call voting became more partisan. Rather, something beyond partisanship systematically influenced the votes for some
members, even while partisanship was intensifying.
25 Notice that the rise of environmental issues is not captured during the time period of our analysis. For abortion and women’s
rights, we observe the “full dynamic”: (1) the issue is structured, if at all, on the first dimension, followed by (2) a period of change
from a potential evolution (second dimension increasingly influences voting), followed by (3) the issue collapsing back onto the first
dimension. Our data on the environment appears to catch the dynamic in period 2 (in Figure 3, at time t∗ ). It turns out that voting
on the environment leading up to the 92nd Congress was not as consistently a first dimensional issue as for the other three issues
when moving into their transitional phases. For instance in the 83rd, 85th, and 87th Congresses, the percent improvement of the
two-dimensional over the one-dimensional model were 5.2, 3.3, and 0.8 percent, respectively. But regardless of the structure of voting
on the environment leading into the 1970s, the pattern after that point is clear: it has increasingly become a first-dimensional issue.
26 Adams (1997) and Wolbrecht (2002) do not suggest, however, any significant differences in the timing of the evolutions. Both
argue that the issue evolutions began in the 1970s. We do not find this to be the case.
17
3.3.3
Gun Control
As for abortion, gun control roll call votes show evidence of systematic influence of the second dimension.
After gun control made a sustained presence of the legislative agenda by the 99th Congress, voting increasingly was structured on the second dimension, reaching a high-point in the 104th Congress. Furthermore,
both votes in that Congress were party votes. Thus, as for abortion, even though voting was highly partisan, some additional factor (dimension) systematically influenced votes. But in the end, gun control fell
back onto the first dimension by the 110th Congress, matching the same pattern as for abortion.
3.3.4
Immigration
Immigration shows quite a bit of variability in the earlier Congresses, in part due to the small number of
roll call votes per Congress. But over time, variability decreases and the issue has become increasingly
one-dimensional. Notice that there is a small interruption in that trend, however, during the 108th and
109th Congresses. That bump in the dimensionality of voting coincides with heightened discussion of immigration reform, which crescendoed with mass protests across the country in 2006. For the most part, the
issue was highly partisan with battle lines largely drawn between the Democratic and Republican parties.
Further analysis, however, shows that party was not the only determining factor of roll call voting.
3.4
A culture war? Graphical examples
We analyze three roll call votes on abortion, gun control, and immigration to help clarify how an issue can
be both highly partisan and influenced by some additional (non-partisan, second) dimension. Doing so also
shows how the small bump for immigration in the 108th and 109th Congresses compares to the larger and
more sustained periods of second-dimension vote classification improvement for abortion and gun control.
• Immigration bill in the 109th Congress: Border Protection, Anti-terrorism, and Illegal Immigration
Control Act of 2005 (H.R. 4437). Yea vote is for more restrictive immigration policy.
• Abortion bill in the 104th Congress: Partial-Birth Abortion Ban Act of 1995 (H.R. 1833). Yea vote is for
more restrictive abortion policy.
• Gun control bill in the 104th Congress: Gun Crime Enforcement and Second Amendment Restoration
Act of 1996 (H.R.125). Yea vote is for less restrictive gun control policy.
Figure 7 plots each House member’s NOMINATE score in the two-dimensional space (that is, using
both the first- and second-dimension scores). We distinguish between three groups: (a) those who were
18
incorrectly classified by the one-dimensional model but correctly classified by the two-dimensional model,
(b) the remainder who voted yea, (c) the remainder who voted nay.
[Figure 7 about here.]
First note that members in the left cloud of NOMINATE scores are Democrats and members in the
right cloud are Republicans, which depicts the well-documented polarized contemporary Congress (e.g.,
Theriault, 2008). For all three roll call votes, the one-dimensional model (roughly) predicts that Democrats
(left cloud) vote nay and Republican (right cloud) vote yea. There are some members from both parties
that are misclassified (squares in the left cloud, dots in the right cloud). Important for our purposes, we
can see a distinct pattern of which members are correctly classified once we account for second-dimension
NOMINATE scores (the X’s) — i.e., which members votes are “corrected” by the two-dimensional model.
For all three votes, notice that there is a cluster of Democrats on the high end of the 2nd-dimension who
are correctly classified in the two-dimensional model, as well as a (smaller) cluster of Republicans on the
low end who are correctly classified once second-dimension scores are included as a predictor. These are
Democrats who are predicted to vote yea once we account for their second dimension score (25 Democrats
for the abortion vote, 37 for gun control, 18 for immigration). For the Republicans, these are members
who are correctly predicted to vote nay once we account for the second dimension (4 Republicans for the
abortion bill, 26 for gun control, and 1 for immigration).
These figures help visualize the differences between a strongly versus weakly two-dimensional issue.
More members’ votes are corrected by the two-dimensional model for the abortion and gun control votes
compared to the immigration vote. These figures also suggest that second-dimension NOMINATE systematically captures some elements of a culture war. We can interpret the y-axis as capturing social/moral
conservatism with higher values as more conservative. In these examples, members who are high on the
y-axis are more likely to vote for more restrictive immigration and abortion policies and less restrictive gun
control. Thus, the claim that moral attitudes influenced roll call voting systematically is somewhat true
— it is captured (to some degree) by second-dimension NOMINATE. The culture war, however, did not
displace traditional politics. Rather we see that it influences (independent of partisanship/first-dimension)
only a handful of members, and the number varies across time and issues.
19
3.5
Changing dimensionality and polarization
How do changes in dimensionality correspond to changes in roll call polarization, which is the measure
relied upon by earlier research on evolutions? We see that the two do not necessarily move lockstep, which
highlights the benefits of considering dimensionality as an additional measure of issue change.
The story for abortion and gun control, and to a lesser extent immigration, is quite different from the
other issues. Whereas voting on the environment and women’s rights polarized as the issue collapsed onto
the first dimension, voting on abortion became increasingly structured onto a cross-cutting dimension as
voting on abortion initially polarized, reaching a pinnacle in the 104th Congress. The same is also true for
gun control. The percent of party vote roll calls and percent improvement from the two-dimensional model
both reach a high point for that issue in the 104th Congress. The patterns for abortion and gun control is
consistent with the strong version of issue evolution. As an issue increased in salience and as elites divided
on the issue, it added something new to political conflict — a second, moral dimension. In a sense, Adams
(1997) was correct to claim a strong evolution at the time of his writing. Since the 104th Congress, however,
voting on abortion has collapsed onto the first dimension and by the 110th is now (essentially) fully a firstdimensional issue. Given the small number of roll calls on immigration, the percentage of roll calls that
are party votes jumps around quite a bit, but our discussion above of an immigration vote in the 109th
Congress is suggestive of a pattern similar to abortion and gun control. Roll call voting was increasingly
explained by some additional factor (dimension) as partisanship on the issue increased.
We summarize these findings in Table 1 by calculating for each issue area the correlation between
the percentage of votes that are party votes (measure of partisanship/polarization) and the percent improvement of the two-dimensional over the one-dimensional model (measure of dimensionality). The correlation is negative for the environment, women’s rights, and budget and tax votes. The less the second
dimension contributes to roll call voting, the more partisan voting is on that issue. This negative correlation
is especially strong among economic votes, which is to be expected since this issue area is the canonical
first-dimensional issue. Abortion, immigration, and gun control, on the other hand, have a positive correlation. As suggested by our earlier observations, the correlation is strongest for abortion (reaching statistical
significance, p < 0.052) and gun control (p < 0.14).
[Table 1 about here.]
20
4
Discussion: Persistence and durability of the party system
Our analysis sheds light on the dynamics of polarization on new cultural issues since the 1970s. Politics on
these issues, as well as more generally speaking, have polarized. Unlike earlier research, which has focused
on observing changes in party polarization on each issue, we show important differences across the issues
in the timing, degree, and persistence of the influence of a second dimension on roll call voting.
Consistent with claims of a rising culture war, the presented empirical patterns suggest that seconddimension NOMINATE systematically captures to some degree a social/moral component. High seconddimension scores are tied to socially conservative values, in our examples for stricter abortion and immigration policies and more lenient gun control laws. This social dimension, however, has not displaced
the classic economic conflicts, contrary to claims of the culture war and (strong) issue evolution perspectives. As depicted in our Figure 7, the second dimension only helps explain a handful of House members,
whereas the vast majority of legislators are still explained by party and economics (first dimension). We
believe that the connections between the various theories of issue change are more fluid than previously
acknowledged. Abortion, gun control, and immigration showed some signs of a strong issue evolution: increased partisanship on the issue (party votes), while also providing something new to the political debate
(second-dimension improvement). An evolution, however, might be a matter of degree: the degree and
length of time to which voting was structured beyond the first dimension varied across those issues.
The fact that those social issues collapsed back onto the first dimension by the 110th Congress is a
testament to the durability of the American two-party system. Not only did these issues bring up a new
dimension of conflict, but the rhetoric was emotionally charged, especially for an issue like abortion. In
spite of this infusion of emotion regarding a newly salient issue and the increased activity among activists,
such as pro-life religious groups, new cultural issues did not drastically disturb the two major parties. For
instance, although socially conservative Democrats voted against the majority of their party in supporting the partial birth abortion bill in the 104th Congress, there was not any fundamental shift in the party
based on that issue. None of the socially conservative Democrats for that vote switched to the Republican
party and only 4 of the 25 Democrats were replaced by their district by a Republican member by the 110th
Congress. As a minority voice in their party, they were not able to instigate any widespread change in the
parties.
The durability of the American two party system is due to many institutional factors, such as the use
of single-member districts for congressional elections and the presidency (for a comprehensive overview,
21
see Aldrich and Lee, 2013). Given the incentives to associate with one of the two major parties (Aldrich
and Bianco, 1992; Aldrich, 1995; Aldrich and Lee, 2013), the best option for these members, who are in a
minority coalition within their party on a subset of issues (i.e., culture war issues), is to stick with their
party. Thus, although new issues may arise and temporarily introduce small splits within the parties, little
opportunity is available for these factions to shift the parties on the issues. For the sake of self-preservation,
the major parties incorporate the new issue into the party system to hold their party together.
We should also acknowledge that our paper has been largely inductive, simply focusing on uncovering patterns of voting over time. We mentioned earlier that we are observing voting on roll call votes, and
we know that observed roll calls are in part a function of agenda-setting. Thus we might expect that the
majority party will try to keep party-splitting votes off of the House floor.27 We did not consider this fact to
be problematic, since agenda-setting is indeed a strategic choice of the parties that they use to shape party
conflict. We leave for future work a more in-depth analysis of cross-issue differences in the ability of the
majority party to control the agenda. Doing so will develop further understanding of exactly how (in terms
of legislative politics and use of institutional tools) issue conflict changes over time.
Racial issues and civil rights through the 1960s and 1970s is the original and arguably the strongest
example of an issue evolution (Carmines and Stimson, 1986, 1989; Carmines, 1991). We consciously have
not considered racial politics in our paper, since there are many significant differences between race and the
issues analyzed in this paper — in sum, the changes surrounding race were more drastic and significant that
for other issues.28 One reason for this difference is that the changing coalitions within the party regarding
race was not limited to a small minority. Changes within the parties was instigated as new coalitions grew
in number in Congress. For instance, absent the influx of new liberal northern Democrats in Congress
to gain majority status within their party, the numbers within the party were too small to instigate any
fundamental party shift on racial politics (Carmines and Stimson, 1989; Rohde, 1991).
27 Cox and McCubbins (2005) for instance talk about the majority party prefers not to get “rolled.” The “Hastert Rule” has also been
a topic of discussion in the media recently.
28 Brady, Juenke and Lee (2011) reconsider the transformative effect of race in the latter half of the 20th century. The basic argument
is that as race (second-dimension NOMINATE) collapsed onto the economic dimension (first-dimension NOMINATE), it transformed
the economic dimension and contributed to the polarizing trend since the 1970s. The argument takes cues from the behavioral literature that has shown how racial attitudes are closely intertwined with economic attitudes (e.g., Kinder and Sanders, 1996; Sears,
Sidanius and Bobo, 2000). Thus, partitioning out “race votes” is not as clear-cut as for the issues studied in this paper. Race can also
affect economic votes. Brady, Juenke and Lee (2011) consider this possibility and attempt to tease out how racial politics contributed
to the polarized Congress.
22
5
Concluding remarks
Whereas previous works focus on overall changes in partisanship on an issue, we consider the additional
characteristic of dimensionality. Doing so contributes to understanding how the varying perspectives on
issue change can complement each other. For instance, the ideological polarization literature tends to ignore issue-specific differences in polarization and dimensionality, often simply noting the aggregate trend
of increased one-dimensionality since the 1970s. We show, however, that the timing and trajectories of issues can differ. Issue evolution, which posits strategic elite behavior as one component, can help explain
these differences. We also demonstrate that considering varying degrees of an issue evolution (comparing,
say, abortion to immigration) can more accurately describe distinguishing features across issues. Doing so
provides a clearer picture of the contemporary culture war.
23
References
Abramowitz, Alan I. 1994. “Issue Evolution Reconsidered: Racial Attitudes and Partisanship in the U.S.
Electorate.” American Journal of Political Science 38(1):1–24.
Adams, Greg D. 1997. “Evidence of an Issue Evolution.” American Journal of Political Science 41(3):718–737.
Aldrich, John H. 1983. “A Spatial Model with Party Activists: Implications for Electoral Dynamics.” Public
Choice 41:63–100.
Aldrich, John H. 1995. Why Parties? The Origin and Transformation of Party Politics in America. Chicago: .
Aldrich, John H. and Daniel J. Lee. 2013. “Why Two Parties? Ambition, Policy, and the Presidency.” Unpublished manuscript.
Aldrich, John H. and William T. Bianco. 1992. “A Game Theoretic Model of Party Affiliation of Candidates
and Office Holders.” Mathematical and Computer Modeling 16:103–115.
Brady, Michael C., Eric Gonzalez Juenke and Daniel J. Lee. 2011. “An Indelible Imprint? Assessing the
Evolution of Racial Politics in Shaping Conflict in Congress during the Civil Rights Era.” Presented at the
2011 Annual Meeting of the American Political Science Association.
Burnham, Walter D. 1970. Critical Elections: And the Mainsprings of American Politics. New York: W.W.
Norton & Company.
Carmines, Edward G. 1991. “The Logic of Party Alignments.” Journal of Theoretical Politics 3(1):65–80.
Carmines, Edward G. and James A. Stimson. 1986. “On the Structure and Sequence of Issue Evolution.”
American Political Science Review 80(3):901–920.
Carmines, Edward G. and James A. Stimson. 1989. Issue Evolution: Race and the Transformation of American
Politics. Princeton, NJ: Princeton University Press.
Carmines, Edward G. and Michael W. Wagner. 2006. “Political Issues and Party Alignments: Assessing the
Issue Evolution Perspective.” Annual Review of Political Science 9:67–81.
Cox, Gary W. and Mathew D. McCubbins. 2005. Setting the Agenda: Responsible Party Government in the U.S.
House of Representatives. New York: Cambridge.
24
Fiorina, Morris P., Samuel J. Abrams and Jeremy Pope. 2005. Culture War? The Myth of a Polarized America.
New York: Pearson Longman.
Frank, Thomas. 2004. What’s the Matter with Kansas? How Conservatives Won the Heart of America. New York:
Henry Holt & Company.
Grose, Christian R. and Antoine Yoshinaka. 2011. “Ideological Hedging in Uncertain Times: Inconsistent
Legislative Representation and Voter Enfranchisement.” British Journal of Political Science 41(4):765–794.
Herron, Michael C. 1999. “Postestimation Uncertainty in Limited Dependent Variable Models.” Political
Analysis 8(1):83–98.
Hetherington, Marc J. 2001. “Resurgent Mass Partisanship: The Role of Elite Polarization.” American Political
Science Review 95(3):619–631.
Hetherington, Marc J. 2009. “Review Article: Putting Polarization in Perspective.” British Journal of Political
Science 39:413–448.
Hunter, James Davison. 1991. Culture Wars: The Struggle to Define America. New York: Basic Books.
Inglehart, Ronald. 1981. “Post-Materialism in an Environment of Insecurity.” American Political Science Review 75(4):880–900.
Inglehart, Ronald and Paul R. Abramson. 1999. “Measuring Postmaterialism.” American Political Science
Review 93(3):665–677.
Karol, David. 2009. Party Position Chang in American Politics. New York: Cambridge University Press.
Key, V.O. 1955. “A Theory of Critical Elections.” Journal of Politics 17:3–18.
Kinder, Donald and Lynn Sanders. 1996. Divided by Color: Racial Politics and Democratic Ideals. Chicago: .
Lauderdale, Benjamin E. 2010. “Unpredictable Voters in Ideal Point Estimation.” Political Analysis 18:151–
171.
Layman, Geoffrey C. and Thomas M. Carsey. 2002. “Party Polarization and “Conflict Extension” in the
American Electorate.” American Journal of Political Science 46(4):786–802.
Layman, Geoffrey C., Thomas M. Carsey, John C. Green, Richard Herrera and Rosalyn Cooperman. 2010.
“Activists and Conflict Extension in American Party Politics.” American Political Science Review 104(2):324–
346.
25
Levendusky, Matthew. 2009. The Partisan Sort: How Liberals Became Democrats and Conservatives Became
Republicans. Chicago: University of Chicago Press.
Lindaman, Kara and Donald P. Haider-Markel. 2002. “Issue Evolution, Political Parties, and the Culture
Wars.” Political Research Quarterly 55(1):91–110.
McCarty, Nolan, Keith T. Poole and Howard Rosenthal. 2006. Polarized America: The Dance of Ideology and
Unequal Riches. Cambridge, MA: MIT Press.
Miller, Gary and Norman Schofield. 2003. “Activists and Partisan Realignment in the United States.” American Political Science Review 97(2):245–260.
Poole, Keith T. and Howard Rosenthal. 2007. Ideology and Congress. New Brunswick, NJ: Transaction Publishers.
Rohde, David W. 1991. Parties and Leaders in the Postreform House. Chicago: University of Chicago Press.
Sears, David, Jim Sidanius and Lawrence Bobo. 2000. Racialized Politics: The Debate About Racism in America.
Chicago: University of Chicago Press.
Shipan, Charles R. and William R. Lowry. 2001. “Environmental Policy and Party Divergence in Congress.”
Political Research Quarterly 54(2):245–263.
Stimson, James A. 2004. Tides of Consent: How Public Opinion Shapes American Politics. New York: Cambridge
University Press.
Sundquist, James L. 1983. Dynamics of the Party System: Alignment and Realignment of Political Parties in the
United States. Washington, D.C.: Brookings Institution.
Theriault, Sean. 2008. Party Polarization in Congress. New York: Cambridge University Press.
Wolbrecht, Christina. 2000. The Politics of Women’s Rights: Parties, Positions, and Change. Princeton, NJ:
Princeton University Press.
Wolbrecht, Christina. 2002. “Explaining Women’s Rights Realignment: Convention Delegates, 1972-1992.”
Political Behavior 24(3):237–282.
26
Appendix A: Spatial depiction of partisan change
To guide our discussion, we refer to a two-dimensional picture of the issue space depicted in Figure 2.
The x-axis is the (traditionally) dominant economic dimension, and the y-axis is some new (orthogonal)
issue. Suppose we can place a legislator in this two-dimensional space, where her location denotes her
ideal policy mix on the x and y dimensions. Based on this spatial framework, what would evidence for an
issue evolution look like?
If the economic dimension is the only important issue dimension for partisan conflict, then the cutting
line that separates Democratic legislators from Republican legislators based on their estimated positions
will be a vertical line, where Democrats are generally located to the left of the line (liberal) and Republicans
are to the right (conservative) (Figure 4.A). If there is a partisan realignment, where the new issue displaces
the economic dimension, then the cutting line will become horizontal, where one party is above and the
other party is below the line (Figure 4.B).29 This perspective is the traditional view of partisan realignment
(see Sundquist, 1983; Miller and Schofield, 2003). The issue evolution perspective argues that the introduction by strategic political elites of a new issue, such as race, can induce such a realignment, which can take
several years and elections to occur.30
[Figure 8 about here.]
As in the main text, the issue evolution perspective does not necessarily call for a complete displacement of the originally dominant dimension. Nonetheless the new issue to some extent transforms the
political landscape, altering the party cleavage in some way. A fairer test, therefore, should allow for such
a middle ground. It could be the case that both the originally dominant and new issue dimensions together
best explain partisan conflict after an evolution. This middle ground scenario is depicted in Figure 4.C.
The new issue may increase in salience, such that the cutting line is not vertical, but does not completely
displace the economic dimension, in which case it is not horizontal either. An issue evolution then realigns
conflict to include both dimensions, where the cutting line is, say, at a 45-degree angle. Notice that one
might also interpret this middle-ground scenario to be conflict extension, but one where the correlation
between issues is not very strong (if it were strong, positions on the new issue would map onto the first
dimension, which is scenario A).
29 Technically speaking, if the new issue completely replaces the first dimension, then that new issue becomes the first dimension in
NOMINATE—i.e., the second dimension in NOMINATE becomes the first (dominant) dimension. For instance, from the realignment
in the 1850s up to the 1870s, (Poole and Rosenthal, 2007, 54) state that the first dimension mainly captures issues of slavery, the Civil
War, and reconstruction.
30 Some traditional views of realignment stress that change largely occurs within a critical election (e.g., Key, 1955; Burnham, 1970).
27
Based on this perspective, McCarty, Poole and Rosenthal (2006) and Poole and Rosenthal (2007) argue that evidence of any issue evolution on racial issues since the 1970s is weak. They show that voting
has become increasingly one-dimensional since the late 1960s. Thus, rather than transform politics, the
importance of the racial (second) dimension has diminished over time.
Appendix B: Number of roll call votes
Table 2 reports the number of votes per issue in each Congress based on the PIPC codings.
[Table 2 about here.]
Appendix C: Overall model fit
In this appendix, we reassess changes in overall model fit to account for the possibility of the second dimension NOMINATE not capturing the cross-cutting conflict of these issues. Accounting for this possibility
does add a bit of nuance and requires revisiting some of our initial impressions. We therefore focus on outlier cases of vote prediction.
We noted in the text that the percentage of abortion votes correctly predicted in the 95th Congress
is extremely low, even when including second dimension NOMINATE. There are two reasons why classification success of a voting model may be low. Success may be low because one might be ignoring the
importance of preferences that are structured on some unmeasured (second, third, fourth, etc.) dimension. It may also be the case, however, that the parties appear split because voting on the issue is simply
chaotic, rather than an outcome of an additional dimension of political conflict. That is, voting might not
fit with a one or two-dimensional (or any-dimensional) spatial model.31 McCarty, Poole and Rosenthal
(2006) and Poole and Rosenthal (2007) show that there was a general dip in the predictive success of the
two-dimensional NOMINATE model during the 1970s, hovering in the mid-80%’s. Since that period, however, the predictability of votes has increased, where the classification rates in recent Congresses are over
90 percent. Thus, the increase in the predictability of abortion votes since a low point in the 95th Congress
is partially due to the low predictability of votes in general during that period. But it also appears that the
increase is due to specific characteristics of the abortion issue — the classification rate is quite a bit lower
31 See Grose and Yoshinaka (2011), who model differences across legislators in their misclassification rates. They are concerned with
what explains unexplained voting behavior. We are interested in, however, what we can explain with spatial preferences. Also see
Lauderdale (2010).
28
for abortion than for other issues in the 95th Congress. The particularly low classification rates of both the
one- and two-dimensional models are consistent with the claim that voting on that issue was cross-cutting,
which is close to the timeline of the evolution (beginning during the late 1970s) proposed by Adams (1997).
But given the striking pattern of the percent improvement of the two-dimensional model, we believe the
significant evolution of the issue did not occur until around 1990, as the issue became increasingly structured off of the first dimension.
Immigration hit a low-point in vote predictability in the 97th Congress, but it does not appear to by
systematically related to issue change. Again, a caveat to our figures is that some Congresses have very few
(if any) votes on an issue, which make some patterns susceptible to potential outliers. First note that the
extremely high classification rates for immigration in the 95th Congress is somewhat an outlier, as it is based
on only one roll call vote (H.R.12443), which passed with near unanimous support by both parties (396-20
vote). Predicting all yeas, therefore, gives high classification rates (396 out of 416 correctly predicted). The
four votes on immigration during the 97th Congress were related to the Immigration Reform and Control
Act of 1982 (H.R.7357), which never reached a final passage vote. Three votes were procedural (passage
of Rules for consideration of the bill, and motions to resolve into the Committee of the Whole). Although
voting on procedural votes tend to be well predicted compared to other types of votes (results omitted),
these particular votes drive the low classification rates for immigration in the 97th Congress (roughly in
the 65 to 75% range). The fourth vote was on an amendment, which split the Democratic majority (106
Democrats for, 80 Democrats against; 4 GOP for, 133 GOP against), was actually well predicted by the oneand two-dimensional NOMINATE models (around 88% correctly predicted).
Women’s rights had especially low predictability even when accounting for the 2nd-dimension relative to other votes (such as our tax and budget baseline) in the 106th Congress.32 Whether this is a systematic
drop or not is not clear with only one roll call vote in that Congress from which to draw conclusions, but we
give a little more consideration here. The women’s rights vote in the 106th (GOP controlled) Congress was
on an amendment (H.Amdt 535/Amendment A002) to H.R. 2 (on education) offered by Mink (D-HI). The
amendment, which was on gender equity and the reauthorization of the Women’s Educational Equity Act,
passed by a 311 to 111 vote.33 On this roll call, the misclassified votes were Republican members who voted
against the amendment when they were predicted to vote for the bill.34 Thus, in this case, a minority Democratic member was able to introduce an amendment (H.R. 2 had a modified open rule [H.Res. 336]) to pass
32 Classification
by the both the one- and two-dimensional models also dips in the 102nd Congress, but that also coincides with a
dip in the tax and budget baseline.
33 The final passage vote on H.R. 2 passed with 358 to 67.
34 65 of 66 misclassified votes were Republican members.
29
over the objection of a majority of the majority (110 of 215 Republican votes were against the amendment).
This example shows how agenda control can minimize the appearance of splits within the party. The
majority party likely prefers to place the agenda items on which the party is in agreement and keep off the
agenda items that the minority prefers and can pass over a divided majority (Cox and McCubbins, 2005).
Thus, the small number of votes on women’s rights (with no votes in some Congresses) might hide the splits
with the parties (in particular the GOP) on the issue. That is, if we do see women’s rights votes, it is precisely
because the majority party is in agreement on the issue. One possibility, therefore, is that women’s rights
was a cross-cutting issue for the few Congresses around the GOP Revolution (103rd through 106th). This
does in fact coincide with a closing of the gender gap among the electorate right around 1992. Notice further
that this also corresponds with the pattern of increased structure on the 2nd-dimension of abortion. There
is therefore some circumstantial evidence of a burgeoning “culture war” (Fiorina, Abrams and Pope, 2005)
— new issues of political conflict changing the political landscape. However, voting on women’s rights
quickly coalesced back onto the first dimension by the 107th Congress with extremely high classification
rates and no contribution of 2nd-dimension NOMINATE scores.
This possibility that agenda control affects observed evolutions, of course, is also relevant for the
other issues in the analysis. The desire to keep off party-splitting issues suggests that our figures might
underestimate the extent to which issues are cross-cutting (and hence evolutions). We do not find this
problematic for our purposes. First, we are most interested in observing changes over time in an issue, since
issue evolution (or more generically, issue change) is a dynamic process. If agenda control is a consistent
tool of the majority party, as Cox and McCubbins (2005) suggest, then cross-Congress comparisons of our
metrics are still instructive for our purposes (i.e., agenda control may shift the classification rates upwards,
but the Congress-to-Congress patterns we observe still show the basic issue dynamics occurring).
Second and more importantly, observing the votes that do make it to the House floor is precisely what
we should analyze to assess issue change, since part of an evolution or change on an issue relates to agenda
control. That is, whether the parties take opposing views on an issue is in part a product of their strategic
choices — how salient will the parties make an issue and will it make it onto the (legislative or campaign)
agenda? For instance, for the canonical example of issue evolution (racial politics in the 1950s and 1960s),
the strategic choice of pushing civil rights onto the agenda was a major contributor to change on that issue
(Carmines and Stimson, 1989). This justifies the use of roll call voting behavior to analyzing issue dynamics
in all previous work on issue change, as well as our own presented analysis.
30
Figure 1: Comparing Levendusky (2009) to Carmines and Stimson (1989)
A. Figure 2.1 in Levendusky (2009, 13)
Elites polarize
↓
Party/ideology mapping is clarified
↓
Ordinary voters see the clarification
↓
Voters sort
B. Figure 7.1 in Carmines and Stimson (1989, 160)
Elite positions
↓
Clarity
↓
Affect toward parties
↓
Mass public alignment
31
Figure 2: Hypothetical correlations between issue-specific preferences and NOMINATE scores over time
A. “Complete” strong issue evolution
correlation ↑
t∗
time →
B. “Partial” strong issue evolution
correlation ↑
t∗
time →
C. Subsumed into first dimension (e.g., weak issue evolution)
correlation ↑
t∗
time →
K EY:
First dimension NOMINATE
Second dimension NOMINATE
32
Figure 3: Correlation between LCV and NOMINATE scores
33
Figure 4: Percent correctly classified: Environmental issues
34
Figure 5: Percent party votes
Note: Party votes are defined as roll calls in which two-thirds (67%) of Democrats vote in opposition to twothirds (67%) of Republicans. Using other thresholds give similar over time patters, although the averages
are higher or lower as expected from using a more or less stringent threshold.
35
Figure 6: Vote classification
A. Percentage of vote correctly classified (by issue area)
B. Percent Improvement: Calculated as the difference between percent classified of the 1-d and 1-d & 2-d
models, divided by percent classified by the 1-d model.
36
Figure 7: Voting and NOMINATE Scores: Which members are influenced by 2nd dimension?
A. Voting on Abortion (H.R. 1833), 104th Congress
B. Voting on Gun Control (H.R. 125), 104th Congress
C. Voting on Immigration Reform (H.R. 4437), 109th Congress
37
Figure 8: Plots of Democrats and Republicans in 2-dimensional space with cutting lines
A. Dominant first dimension
y
D
R
x
B. Dominant second dimension
y
D
R
x
C. Equal weight of first and second dimensions
y
D
R
x
38
Table 1: Correlation between percent party votes and percent improvement of two-dimensional model
Issue # obs Correlation
Environment
19
-0.3307
Women
10
-0.2721
Gun
10
0.5026
Abortion
18
0.4646†
Immigration
15
0.3338
Tax
19
-0.8830†
† Significant at 10% level.
39
Table 2: Number of roll calls per Congress
Congress Envir. Women Gun Abortion
92
52
4
0
0
93
70
1
0
3
94
116
3
0
4
125
6
0
16
95
96
74
0
0
8
97
53
0
0
2
98
69
2
0
3
99
42
2
8
5
100
64
0
2
7
70
0
2
5
101
102
57
5
7
12
103
92
0
7
17
104
70
0
2
16
105
74
0
1
20
106
105
1
20
8
107
24
1
0
12
108
34
0
6
6
109
55
1
3
10
110
162
8
7
3
Note: Based on PIPC Roll Call Database
40
Immig.
2
8
0
1
1
4
19
16
3
17
0
0
20
0
2
12
6
21
4
Budg./Tax
55
122
148
238
220
134
104
98
93
108
154
113
154
128
166
143
178
146
162