Two-stage electoral competition in two-party contests: persistent divergence of party positions

Models of party competition building on Downs (1957) have recognized that there are centrifugal and centripetal forces in party competition; but one such force, the existence of party primaries, has been remarkably neglected in recent literature. We consider party/candidate policy divergence in two-party competition in one dimension where there is a two-stage electoral process, e.g., a primary election (or caucus) among party supporters to select that party's candidate followed by a general election. We develop a model in which (some or all) voters in the primary election are concerned with the likelihood that the primary victor will be able to win the general election and being concerned with that candidate's policy position. This model is similar in all but technical details to that given in an almost totally neglected early paper in Public Choice Coleman (1971) 11:35-60, but we offer important new results on electoral dynamics for candidate locations. In addition to accounting for persistent party divergence by incorporating a more realistic model of the institutions that govern elections in the U.S., the model we offer gives rise to predictions that match a number of important aspects of empirical reality such as frequent victories for incumbents and greater than otherwise expected electoral success for the minority party in situations where that party has its supporters more closely clustered ideologically than the supporters of the larger party (in particular, with a concentration of voters between the party mean and the population mean).