Executive Summary

The congressional primary is often portrayed as a central agent in the story of hyper-partisan polarization in the United States and congressional politics in particular. This has led reformers to explore the possibility that primary reform, particularly open and nonpartisan primaries, could be a promising mechanism to elevate more moderate and compromise-oriented candidates and representatives.

This report offers an analytical overview of recent scholarship on the effects of the primary election on politics and the effects of different primary rules on voters, candidates, and policy moderation. Though many studies have been conducted in recent years, this is the first time that they have been systematically brought together with the express purpose of drawing comprehensive lessons.

The broad takeaway is that while primary elections are likely contributors to hyper-partisanship, their impact is more marginal than many popular accounts suggest. Similarly, primary reform thus far has had very limited impact. At best, existing studies have found only marginal effects on voters, candidates, and electoral winners across different types of primaries—including the much-discussed California top-two primary.

Yet research does show that primaries incentivize more polarizing behavior among candidates and legislators. There is ample evidence that fear of a primary challenge leads candidates to reject compromise; to cultivate and stay close to their primary constituencies and the interests groups and donors who actively fund candidates in primaries; and to engage in partisan conflict to prove their bona fides to their primary constituencies. Driving this fear, in large part, is the assumption that primary electorates are more ideologically extreme than general election electorates. However, findings in support of this assumption are somewhat mixed, and may be distracting us from the deeper, more troubling divide that exists between Democratic and Republican electorates.

Indeed, primary electorates are probably a little more extreme than general election electorates, but whatever difference exists between them is dwarfed by the difference between Democratic and Republican electorates. There is not some latent fifth column of sensible moderate voters reluctantly waiting in the wings. The vast majority of voters have sorted into the two teams on offer.

The forces driving hyper-partisan polarization appear to be deeper than primary reform can reach. With the two parties already so far apart, and a winner-take-all electoral system that increasingly rewards extremity, there are simply very few opportunities for would-be moderates to gain traction. And few would-be moderate politicians have the desire to fight a losing battle.

Certainly, existing studies have their limits. This report concludes with a series of recommendations for new research approaches and new types of data that could help answer some of our unresolved questions. It also looks forward to the innovation and potential spread of the top-four open primary in Alaska. Though we need to assess its impact in the real world, there are at least theoretical reasons why this model might incentivize compromise-oriented politicians seeking to build more inclusive electoral coalitions.

Those seeking greater insight into the potential for primary reform will find there is much to learn from a comprehensive analysis of recent scholarship on primary elections. But beyond that scope, the extensive research on this topic provides a unique window into the structure of partisan competition in America, and the challenges of countering hyper-partisan polarization at this critical moment for our democracy.