SSN Key Findings

Do Primary Elections Promote Extremism in U.S. Politics?

Policy field

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Clark University

This brief was originally published on June 20th, 2014. It has been updated with new analysis for the 2020 election.

U.S. congressional primary elections have faced a lot of criticism from analysts and media commentators, who argue that these contests discourage moderation and bipartisanship. Incumbent members of the House and Senate are said to be dissuaded from searching for bipartisan solutions to national problems because they fear they could be outflanked by more extreme challengers in party primaries. Because many Americans do not vote in primaries, the voters who turn out are allegedly more ideologically extreme. Fearing challengers who may attract such voters, the story goes, incumbent officeholders shy away from moderate positions and legislative compromises. In the general elections, consequently, majorities of relatively moderate voters are forced to choose between candidates who pose ideologically extreme choices. 

Although there have been several high profile primary challenges in recent years, my research suggests that this received wisdom is largely incorrect. Primary challenges have become more common but successful ones have not, and if incumbents fear primaries more today, their qualms are based more on what they hear about primaries than on what actually takes place in these elections. 

Are Primary Challenges Becoming More Frequent? 

Over the past four decades, it turns out that there has been an increase in the number of challenges, but not in the proportion of successful challenges. 

• In elections to the House of Representatives, somewhat competitive primary challenges (races where the incumbents were held to 75% or less of the vote) increased from an average of 26 per year in the 2000s to an average of 67 per year during the 2010s. The increase was entirely driven by Republicans; the number of Democratic challenges was slightly higher than in the 2000s but lower than it had been in the 1970s, 1980s, or 1990s.

• In the Senate, the number of challenges fluctuates but there is no evidence of a trend. 

• Defeats of incumbents are rare, and it is very rare for a successful challenger to go on to win the general election. In years with no redistricting, no more than three or four Congressional incumbents are likely to lose their primaries. Four House incumbents lost their primaries in 2018. For the Senate, 2002 was the last election in which a successful primary challenger went on to win the seat. 

When Challenges Increase 

Upticks in primary challenges usually coincide with an increase in a party’s number of general election victories in a given year. 

• In 1974, overall Democratic general election gains were accompanied by a large number of primary challenges to incumbents, often from anti-war candidates or other liberals. 

• In 1994, GOP general election gains followed many primary challenges from candidates accusing Republican incumbents of being too willing to work with President Bill Clinton. 

• In 2006 and 2008, Democrats gained seats in the House after many contested primaries where incumbents were criticized for not doing more to oppose the Iraq War or the priorities of the George W. Bush administration. Recent upticks in Republican primary challenges since 2010 fit this same pattern. 

• In 2010, the Tea Party wave inspired many challenges to moderate Republicans; this movement persisted in 2012 and 2014. Tea Party activists claimed credit for the primary defeat of House Majority Leader Eric Cantor.

Primary challenges are not all the same. Recently, attention has focused on ideological challenges – where incumbent Democrats are challenged from the left or incumbent Republicans are challenged from the right. But primary contests are not usually about ideology. Challengers usually target incumbents who are accused of ethical lapses or otherwise embroiled in political or personal scandals, or they challenge incumbents showing signs of infirmity or incompetence. 

What is Different Now? 

Why is it, then, that primary challenges have commanded greater attention in recent years? Although most bids are unsuccessful, each of the past five election cycles has featured a few high-profile challengers (such as Kelli Ward’s 2016 challenge to Sen. John McCain, in Arizona, and Alexandria Ocasio-Cortez’s 2018 challenge to Rep. Joe Crowley, in New York) who have: 

Framed their races as referenda on their party’s ideological purity. Seeking to present themselves as unorthodox candidates or “anti-politicians,” they have adopted extreme stances and run advertisements designed to set them apart from “conventional” politicians. 

Raised substantial amounts of money nationwide – either from small contributors or from major donors outside of their states or districts. 

Garnered support from ideological, multi-issue interest groups (such as Justice Democrats or the Club for Growth) that have long sought to push their parties away from the center. For such groups, media attention is more important than whether their candidate actually wins. 

Since 2010, high-profile ideological challenges have been more common in the Republican Party because Democratic multi-issue groups have concentrated on protecting vulnerable incumbents. Despite an increase in Democratic primary challenges in 2018, challenges were still far more frequent among Republicans. Ideological challenges in each party also tend to take on a different focus. Leftist Democratic challengers tend to criticize the relatively moderate voting records of the incumbents they face, whereas GOP challengers from the right criticize incumbents’ demeanor – for example, willingness to compromise – more than their typically conservative voting records. 

Improving Primary Elections 

In sum, there is no reason to conclude that U.S. primary elections are driving ideological polarization or preventing compromise in Congress. Some incumbents may be reacting fearfully to a few high profile contests, but it is hard to argue that primary challenges should cease. Nevertheless, media coverage could improve. Primaries are low-visibility elections in which voter turnout can be low and unrepresentative. If media reports focused less on a few sensational contests and instead offered fuller information about candidate records and sources of financial support, voters in all competitive primaries would be better able to make informed decisions.

Read more in Robert G. Boatright, Getting Primarried: The Changing Politics of Congressional Primary Challenges (University of Michigan Press, 2013).