Modeling the electoral dynamics of party polarization in two-party legislatures

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 dramatically 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 partisan 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.

Cracking the whip: spatial voting with party discipline and voter polarization

“…Some evidence exists that geographic polarization-the sorting of voters into left and right states, and the type of polarization relevant for this study-has increased since the 1980s (see Sussell and Thomson (2015), though for a more skeptical take see Fiorina and Abrams (2008)). Consistent with the model presented herein, party platform divergence generally also is thought to have increased over the same period (for example, see Barber and McCarty (2013) and Merrill et al (2014)). Trends in the whip rate are rather harder to measure, with researchers tending to focus on more easily measurable party unity scores.…”

Perspectives on the Comparative Study of Electoral Systems

“…Today, as at the end of the 19th century, party differentiation both at the constituency level and in Congress is extreme. Recent work has attempted to model the factors that can explain why we observe variation in ideological divergence without any change in electoral system rules (see Merrill et al 2014 andBrunell et al 2016a,b for more extended discussion and literature review).…”

Components of party polarization in the US House of Representatives

“…Estimation of w from data will be specified in Section 3. The weighting factor w may vary over time, depending on factors such as the degree of national party discipline (see Merrill et al, 2014). Note that the two candidate positions will not be equidistant from the district median (one on either side) unless the district median is such that the two national party positions are equidistant from it.…”

“…However, none of the models of polarization above do what we want to do in this essay, namely link what we see at the district level to what is happening in the legislature as a whole. McCarty et al (2009), and Merrill et al (2014), however, take an approach that we can build on. In particular, the latter propose a model that relates congressional polarization with constraints on district candidates' ability to locate at positions far from the national party stance that may be imposed by voter perceptions of credible locations and by activist involvement in the candidate selection process.…”

“…The distance between the platform a candidate offers and the location of the median voter in her/his constituency is constrained by national party positions given a lack of credibility with voters for party candidates who claim to locates themselves far from the national party position, but also by the reluctance of party voters and activists to nominate candidates too far from the national position (Merrill et al, 2014;Winer et al, forthcoming), especially insofar as the national parties have already taken polarized positions. We can see direct examples of the difficulty facing candidates who seek to moderate their position away from the national party position to move closer to their own district's median, when we consider Tea Party challenges to Republican incumbents.…”