Abstract
This study investigates whether primary election structure influences the ideological positioning of U.S. Senate candidates, thus contributing to legislative polarization. It tests two hypotheses. First, that closed primaries produce more ideologically extreme candidates than semi-closed or open systems. Second, that these effects intensify after the 2010 Supreme Court decision in Citizens United v. FEC, which is used as a structural break to contextualize this analysis. Using data from twelve states between 2000 and 2020, clustered regression models estimate the effects of primary type, party affiliation, and the post–Citizens United period on DW-NOMINATE scores, controlling for incumbency and electoral competitiveness. The results show that party affiliation is the strongest and most consistent predictor of ideological extremity. Primary structure exhibits conditional effects, providing limited support for the argument that closed systems intensify ideological positioning. While Citizens United does not produce a strong immediate shift, lagged models suggest potential delayed effects. Overall, the findings indicate that partisan dynamics play a larger role in shaping polarization than primary election structure alone.
Advisor
Kim, Sekwan
Department
Political Science
Recommended Citation
Reckard, Hadley, "The Primary Problem: How Nomination Rules Shape America's Political Divisions" (2026). Senior Independent Study Theses. Paper 13392.
https://openworks.wooster.edu/independentstudy/13392
Disciplines
American Politics
Publication Date
2026
Degree Granted
Bachelor of Arts
Document Type
Senior Independent Study Thesis
© Copyright 2026 Hadley Reckard