Journal of Political Institutions and Political Economy > Vol 1 > Issue 2

Reducing Legislative Polarization: Top-Two and Open Primaries Are Associated with More Moderate Legislators

Christian R. Grose, Department of Political Science, University of Southern California, USA,
Suggested Citation
Christian R. Grose (2020), "Reducing Legislative Polarization: Top-Two and Open Primaries Are Associated with More Moderate Legislators", Journal of Political Institutions and Political Economy: Vol. 1: No. 2, pp 267-287.

Publication Date: 11 Jun 2020
© 2020 C. R. Grose
Elections,  Legislatures,  Campaigns
Electoral institutionsopen primarieselection administrationCongressideology


Login to download a free copy
In this article:
Theory: Primary Election Rules Influence Legislator Roll-Call Voting 
The Top-Two Open Primary: A Radically Different Way of Administering Primaries 
Party Cues for Voters Differ in the Top-Two Primary Compared to Other Systems 
Open Primaries and Closed Primaries 
Methods and Analysis 
Other Independent Variables 
Results: The Top-Two Primary Is Associated with Less Extreme Legislators 
Are Incumbents Adapting to New Primary Systems or Are New Members Less Extreme? 
Conclusions and Implications 


Partisan polarization in Congress is at its highest levels in more than 100 years. Political reformers advocate for changes to electoral institutions in order to reduce legislative ideological extremity, yet political scientists have been surprisingly skeptical that changes to primary nomination systems affect legislator ideology. I theorize that electoral systems shape legislator ideology. The top-two primary — used in just under one-fifth of all U.S. House elections — incentivizes legislators to moderate. Empirically, I rely on exogenous changes in the introduction and withdrawal of the top-two primary due to ballot proposition or in response to court cases, and examine legislator ideological extremity from 2003 to 2018. The top-two primary has reduced ideological extremity among legislators, relative to those elected in closed primary systems. Legislators elected in open primaries also show some evidence of attenuated extremity. This ideological moderation in top-two and open primaries is found among both incumbents and newly elected legislators.



Journal of Political Institutions and Political Economy, Volume 1, Issue 2 Special issue - Election Administration and Technology
See the other articles that are part of this special issue.