Modeling the electoral dynamics of party polarization in two-party legislatures
| DOI | 10.1177/0951629813508847 |
| Author | Thomas L Brunell,Bernard Grofman,Samuel Merrill |
| Published date | 01 October 2014 |
| Date | 01 October 2014 |
| Subject Matter | Articles |
Article
Modeling the electoral
dynamics of party polarization
in two-party legislatures
Journal of Theoretical Politics
2014, Vol. 26(4) 548–572
©The Author(s) 2013
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DOI:10.1177/0951629813508847
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Samuel Merrill, III
Department of Mathematics and Computer Science,
Wilkes University, Wilkes-Barre, PA, USA
Bernard Grofman
Department of Political Science, and Center for the Study of Democracy,
University of California, Irvine, CA, USA
Thomas L Brunell
School of Economic, Political and Policy Sciences, University of Texas at Dallas,
Richardson, TX, USA
Abstract
While there are many formal models that generate predictions about polarization, only a handful
address the question of how, with no change in electoral rules, levels of polarization can dramat-
ically vary over time, as they have in the US House during 150 years of two-party competition.
We propose a model that emphasizes national party constraints on district candidates’ ability
to locate at positions far from the national party stance. The model predicts a close relation
between tight tethers maintained by the national parties and congressional polarization, suggests
implications for political competition, and generates the empirically accurate prediction that par-
tisan polarization and within-party differentiation are negatively correlated. When the tethers of
the two parties are not equally strong, the model suggests modifications to the conditional party
governance approach and helps explain ideological shift/drift affecting both parties, with the party
with the tighter tether moving the other party toward its ideological wake.
Keywords
Congressional polarization; electoral dynamics; legislature; party polarization; US House
Corresponding author:
Samuel Merrill, III, 3024 43rd CE, NW, Olympia, WA 98508, USA.
Email: smerrill@mathcs.wilkes.edu
Merrill III et al. 549
1. Introduction
Ideological polarization and partisan enmity is arguably the driving force of the past
several decades of US electoral history. But, while there are many formal models that
generate predictions about polarization, only a handful address the question of how, with
only limited change in electoral rules, levels of polarization can dramatically vary over
time, as in fact they have in the US House over the course of more than 150 years of
two-party competition (McCarty et al., 2006; and see below). Virtually all the work that
seeks to provide a dynamic perspective on congressional polarization looks at macro-
level factors such as changes in immigration levels or economic inequality.
Our approach is quite different, and is based on the interplay between national party
expectations and constituency level electoral dynamics. We seek a model that can relate
electoral dynamics to party discipline and district ideology.
We model replacement dynamics in terms of the ideological wiggle room that par-
ties permit their candidates to (credibly) locate at positions close to those of the median
voter in the constituency. We explore national party tethers that can constrain the fea-
sible range of party competition about each national party position (which we specify
empirically as the mean ideological position of the party delegation in the current legis-
lature, specifically the average DW-NOMINATE score). Our model generates changing
party polarization endogenously and predicts that partisan polarization and within-party
differentiation are negatively correlated. Furthermore, the model allows for asymmetry
in tether strength. We show that, if one of two national parties exerts a tighter tether than
the other, both partisan delegations can shift significantly in the direction of the party
exercising the tighter tether. These results have important implications for the structure
of political competition at the constituency level, and the nature of party polarization in
the legislature and, thus, for conditions under which conditional party governance will
be met (see Aldrich and Rohde, 1998; Aldrich et al., 2007; Rohde, 1991). In particular,
we show that if one party is more ideologically rigid than the other, its cohesiveness has
impact on the distribution of policy positions taken by members of the other party.
1.1. Literature review: explaining party positioning at the constituency level
There have been numerous models of ideological differentiation in two-party contests,
beginning with Downs’s seminal (1957) model, which was generally interpreted as pre-
dicting tweedledum, tweedledee politics in any constituency. New models challenged the
assumption that politicians cared only about reelection and not about policy (Wittman,
1973, 1977, 1983). Winer et al. (2009) define models in terms of where they fit on a
continuum that has two opposite poles. At the office-seeking extreme, each candidate,
regardless of party, will offer a platform that is identical to the preferences of the median
voter in the district in which s/he is competing. At the partisan policy-seeking extreme,
each party’s candidates will offer a platform that will be invariant with respect to district
or, to paraphrase Gertrude Stein, ‘A Democrat is a Democrat is a Democrat; a Republican
is a Republican is a Republican’ (Winer et al., 2009).
The empirical reality is apt to be in between. National parties are typically moti-
vated by both office-seeking and policy-seekingobjectives (Adams et al., 2005; Wittman,
1973), and hence seek optimal ideological or issue positions that are separated from one
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