The 2018 Primaries Project: Introduction to the candidates

A woman wears a sticker in multiple languages after voting in the primary election at a polling station in Venice, Los Angeles, California, U.S. June 5, 2018. REUTERS/Lucy Nicholson - RC1BF5D43BD0
Editor's note:

The following is the first section of “Political polarization and congressional candidates in the 2018 primaries,” a report from The Primaries Project at Brookings.

In the midterm elections of 2010, the Tea Party assault on Republican Party incumbents was successful enough to create within the House Republican Conference a group of insurgents whose uncompromising positions on issues shut down the government, drove a Speaker of the House from office, and opened up an era of even more intense dysfunction in the Congress. Since then, more journalists and scholars have come to realize that to understand politics in a country where the political parties are “big tents,” one needs to appreciate the important role that factional divisions within parties play.

When we began The Primaries Project in 2014, we called congressional primaries “the stepchild of election studies” because journalists and scholars largely ignored them. Since then, however, more and more people have realized that the key to understanding factions in American political parties is to understand congressional primaries. Even though contested congressional primaries are rare and even though incumbent defeats in primaries are even more rare, factional divides within a party manifest themselves in primaries, and the existence of those factions shapes the behavior of members of Congress—even when they are not being directly challenged themselves. Thus, in establishing The Primaries Project four years ago, we set out to understand the dynamics within each political party and the different factions’ impact on the policy agenda—regardless of whether those factions were winners or losers.

2018 saw 2,280 total primary congressional candidates running for office, including over 2,000 House candidates—an increase of nearly 500 over the 2016 cycle. Democratic House candidates largely drove this increase.

In 2014, we started tracking the characteristics and issue positions of every candidate who appeared on a congressional primary ballot by coding their websites. (Detail on our methodology can be found in the Appendix.) This coding included incumbents, their challengers, and those running for open seats. As Table 1 displays, this resulted in a dataset of 1,662 total congressional candidates, including 1,443 House candidates. When we repeated this study in 2016, we found a few more candidates running for federal office: 1,781 total congressional candidates, including 1,550 House candidates. In 2018, we saw an even greater increase. 2018 saw 2,280 total primary congressional candidates running for office, including over 2,000 House candidates—an increase of nearly 500 over the 2016 cycle. Democratic House candidates largely drove this increase. (While the focus of The Primaries Project is on Republicans and Democrats, we also track minor party and independent candidates in top-two primary states because they run on ballots alongside these major party candidates. For more details, please visit the Appendix.)

Table 1: Number of primary candidates running for Congress, 2014-2018

2014 2016 2018
Total 1662 1781 2280
House candidates 1443 1550 2009
GOP House candidates 755 812 874
DEM House candidates 646 700 1077

In addition to this large uptick of Democratic congressional primary candidates, we also find that a greater share of incumbent Democrats were “primaried” this cycle compared to previous years. While the percentage of incumbent Republicans receiving primary challenges has remained consistent since the 2010 midterms, Democrats have seen much greater variation. In the last midterm election, fewer than 28 percent of Democratic House incumbents were challenged, but in 2018, this figure rose to 45 percent. This recent uptick is especially significant given that the Democratic Caucus in the House is quite small by modern historical standards.

Despite this influx of energized candidates, the 2018 primary cycle saw few surprises when it came to incumbent challenges. As Table 2 indicates, this election cycle has been similar to years past, with only four incumbents losing their nominations: Democrats Mike Capuano (Mass.-7) and Joe Crowley (N.Y.-14) and Republicans Robert Pittenger (N.C.-9) and Mark Sanford (S.C.-1). Much ink has been spilled this cycle on incumbent losses. When progressive candidates beat long time incumbents in New York and Massachusetts, they gained instant fame. And when President Trump took down a Freedom Caucus member from South Carolina, it too became big news. However, as we will see, the headlines that these wins triggered are hardly representative of any broader trends.

Table 2: Number of House incumbents losing in primaries, 2004-2018

2004 2006 2008 2010 2012 2014 2016 2018
Republicans 0 1 3 2 6 3 3 2
Democrats 2 1 1 2 7 1 2 2

In his influential 1974 article, “Congressional Elections: The Case of the Vanishing Marginals,” David Mayhew draws attention to how congressional incumbents had been increasingly running up the score in general elections. Like Mayhew, we seek to draw attention to incumbents’ margins—but this time, looking at incumbent candidates’ primary election performances. Analyzing the past six primary election cycles, we find that few marginals exist here, too. Overall, our findings indicate that incumbents of both parties continue to dominate their primary challengers; however, we do note a slightly asymmetric finding across the parties.

The findings from Figure 2 confirm that, despite increased energy among candidates and increased numbers of congressional candidates, incumbent members of Congress are continuing to fare well whenever challenged. Even in light of record numbers of primary candidates, incumbents continue to run up the score. As Figure 2 shows, the average contested Democratic incumbent won her race by nearly 57 percent. Compared to 2016, primary elections this cycle were actually slightly less competitive for incumbents. On the Republican side, the uptick in margins is difficult to explain conclusively from our data. However, one possibility is that Republican incumbents have gotten better at dealing with the new, more conservative wing of the party, and thus were able to avoid attracting strong challengers. Consistent with Robert Boatright’s “Getting Primaried(2013), the newest margins data add to the evidence that surprises in primary elections continue to be rare for incumbents, despite the disproportionate post hoc media attention an electoral surprise receives.

This election cycle has been similar to years past, with only four incumbents losing their nominations.

Nonetheless, the purpose of our study is to move beyond the standard metrics of winning and losing. In spite of consistent findings, it is clear that politicians themselves pay a great deal of attention to their primary opponents and to the possibility of having a primary opponent. Furthermore, the purpose of The Primaries Project has been to understand the internal factions in each major American political party, and there is no better way to do so than by looking at who runs in primaries—and what they are saying. To do that, we have divided our data into the following categories, using the same organization as our previous two studies. We will seek to answer the following questions:

  • Who runs in congressional primaries?
  • What are the internal divisions within each party?
  • What are the candidates talking about and what are they not talking about?

Continue to the next section, “Who runs in congressional primaries?”


  • Footnotes
    1. See: Elaine C Kamarck and James R. Wallner, “Anticipating Trouble: Congressional Primaries and Incumbent Behavior,” forthcoming, Brookings, September, 2018.
    2. The average incumbent’s percent of the vote subtracted by her top challenger’s percent of the vote was 57%. (For example, in a two-person primary, a 57% margin of victory means the incumbent received 78.5% of the vote and her challenger received 21.5% of the vote.)