Introduction

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. The story goes something like this: In primary elections, especially “closed” primaries (in which only registered partisans can vote), only the most extreme partisan voters participate. To win over these ideological partisans, candidates adopt combative rhetoric and extreme policy positions, while moderates are shut out.

Within this framing, the straightforward solution appears to be primary reform. Different primary rules, in theory, could create different pathways for would-be moderates and compromisers to attain elected office. In particular, the idea of “open” and “nonpartisan” primaries (in which all voters can participate, regardless of party affiliation) has captured the imagination of many reformers and good government politicians.¹

There are good reasons why primary elections have become an increasingly attractive target for reform in recent years. Chief among them is that districts are more politically lopsided than ever, to the extent that roughly five out of every six congressional districts voters are so solidly Democratic or Republican that the only election that matters is the primary election.² This trend toward “safe districts” is largely a product of geographic sorting of the parties, and an important driver of partisan polarization. When districts are highly partisan, their representatives will likely be highly partisan too.

Any theory of representation would expect this degree of district lopsidedness to lead to greater polarization among elected representatives, with or without primary elections. But primaries are seen as an accelerant to polarization because the Democrat or Republican who seeks to represent a district must also survive a primary election. Especially in lopsided districts, winning the primary is tantamount to winning the general election, no matter how extreme the candidate.³ In this environment, many have turned to primary reform for hope, seeing primary rules as relatively open to change.

But is primary reform as promising as its advocates argue? Is the congressional primary election as responsible for hyper-partisan polarization as its critics claim? Are there feasible and productive paths forward for primary reform? Or is primary reform a dead end and a waste of energy? In other words, is the congressional primary the polarizing force it has been made out to be, and if so, can it be redeemed?

This report attempts to tackle these questions by providing an analytical overview of recent scholarship on the effects of the primary election on U.S. politics, and the effects of different primary rules on voters, candidates, and policy moderation. In doing so, this report offers a more complicated take on the conventional wisdom that primaries are to blame for polarization and that reforming them is a powerful lever for political change. Broadly, the research shows that primary elections are likely contributors to hyper-partisanship, but their impact is more marginal than many popular accounts suggest. Similarly, primary reform may not be as promising as its advocates propose. At best, existing studies have found only marginal effects of primary reform—especially the much-discussed California top-two primary—in promoting more moderation in politics.

Most studies and analyses discussed in this report have appeared in peer-reviewed academic journals over the last decade (approximately); all of them come from respected political scientists. Admittedly, this report does not encompass the totality of studies on primaries and primary reform. However, primaries and primary reform are topics that have been well-studied by political scientists in recent history, and they have generated relatively consistent conclusions.