How Strong Should Our Party Be? Party Member Preferences Over Party Cohesion

Abstract

In this article, we seek to explain when and why political parties pressure their members to vote with the party. We model party cohesion as an endogenous choice of preference alignment by party members. Couched in Krehbiel's (1996, 1998) pivotal politics model, the formal theory advanced here shows party cohesion to be related to the initial preference alignment of party members, the divergence in preferences between parties, the cohesion of the opposing party, the party's size, and the party's majority or minority status. We solved the model analytically for generalized‐partial equilibrium results and further analyzed it through computer simulations. We tested the model's predictions in the U.S. Senate using Rice party cohesion scores from the 46th through 104th Congresses. The data analyses show strong support for this theory of endogenous choice of party pressure.