Researchers Follow the Money to Illuminate US House Candidates’ Ideological Movement

This article is cross-posted at NYU.

It’s well-known that many political candidates campaign to match the ideologies of their parties in primary elections before moving back to the center during the general-election period. However, a new study by New York University’s Center for Social Media and Politics finds that this shift is much more likely to occur when an incumbent holding a safe congressional seat is facing a well-funded primary challenger.

“Social media has made it easier for primary challengers to raise money and reach voters, making strong, well-financed competition more likely for incumbents,” says Maggie Macdonald, the lead author of the paper, which appears in the journal Electoral Studies.

“At the same time, our partisan and polarized environment has led to more safe congressional seats, often making the primary race the most important election in most districts,” adds Macdonald, who conducted the research as a postdoctoral fellow at the Center for Social Media and Politics (CSMaP) and is now an assistant professor in the University of Kentucky’s Department of Political Science. “In this landscape, candidates must decide how much to adjust their messaging in order to appeal to both primary and general-election voters.”

Few US House seats are competitive today — fewer than 70 out of 435 races in 2024, according to the Cook Political Report — meaning that the majority of the competition an incumbent will face when running for re-election is the primary, where opponents are members of the same party.

While observers have long noted that candidates move to the center after their primary elections, the circumstances under which they do so is less understood.

In taking a closer look at this phenomenon, CSMaP researchers examined 2020 US House campaigns — 158 Republicans and 212 Democrats — to determine if incumbents facing a viable primary challenger moved to a more extreme messaging ideology in the 2020 pre-primary period than they signaled in 2019 and whether the extent of this movement was larger in safe districts than in competitive districts. Viability of challengers was measured based on whether or not the challenger was well-funded — raising $100,000 or more in in-state contributions.

To measure ideological movement over time, the researchers considered incumbents’ Twitter (now “X”) posts in 2019 and 2020, using an established method, developed by CSMaP in previous work, for measuring the ideology of URLs shared by a social-media user. Specifically, they analyzed posts from the beginning of the 116th Congress in 2019 and two other periods: the 2020 pre-primary period (the three months leading up to the primary election) and the three months leading up to the general election that November (Notably, posts by then-House Speaker and Democrat Nancy Pelosi fell close to the median of her party while those by then-Minority Leader and Republican Kevin McCarthy were further to the right of his party’s median).

“With our measures of candidate messaging ideology, we were able to pick up on changes in campaign behavior on Twitter over even small time periods,” explains Megan A. Brown, a CSMaP research scientist at the time of the study and now a doctoral student at the University of Michigan.

The authors also took into account whether or not the incumbent held a “safe” seat, using the Cook Political Report’s ratings as a barometer.

The results showed that when confronted with a well-funded primary challenger, both Democratic and Republican incumbents in safe seats moved toward ideological extremes in the three months before the primary, compared to their behavior at the start of the campaign in 2019. By contrast, competitive-seat incumbents showed no such change, nor did those who did not face a well-funded primary challenger. In addition, those safe-seat incumbents of both parties who moved toward the extreme in the pre-primary period became more moderate after the primary than did those candidates who showed no such ideological movement after 2019.

“Once the incumbent crossed the main hurdle to their re-election — a primary against a well-funded challenger — they were free to return closer to the original ideology expressed at the very beginning of their campaign in 2019,” adds NYU Professor Jonathan Nagler, co-author of the study and co-director of CSMaP.

The study’s other author was NYU Julius Silver Professor Joshua A. Tucker, co-director of CSMaP.