Why are so many candidates backed by President Donald Trump unseating incumbents this primary election season? Some political analysts say the primary wins are proof that the president has significant power to tell Republican voters what to do. But research from Washington University in St. Louis points to an additional form of presidential power that has been overlooked.
In a working paper, “The Party’s Disappointed Dropouts: Presidential Nominations and Participation in Future Primary Elections,” Daniel Butler, a professor of political science in Arts & Sciences, provides evidence that primary donors and voters who dislike the winning presidential primary candidate are less likely to donate and participate in future party primaries.
This research suggests that Trump-aligned candidates are advancing because disenfranchised Republican voters — those who supported Nikki Haley, Ron DeSantis or Vivek Ramaswamy in 2024 — are significantly less likely to participate in this year’s intraparty contests. It could be that these voters dislike the policy direction the party is heading, or because they feel less psychological attachment to the party. As a result, the president’s supporters are disproportionately represented in the primaries, Butler explained.
“Our research shows that people are selecting out of the primary process, which means there is little opposition to the president within the party,” Butler said. “This self-selection out of the primary process has empowered Trump. The more moderate Republicans are not showing up to vote for the Thomas Massies and John Cornyns of the party.”
Using data on campaign donors between 1984 and 2020 and the American National Election Study panel from 2016-2020, the authors showed that this phenomenon has occurred in 12 of 14 previous elections, including both Democratic and Republican races. But while previous presidents have stayed out of primary contests and tried not to influence the outcomes, Trump has chosen a different route. Trump’s support of primary challenges to members of his own party is a big shift in American politics, Butler said.
A new political calculus
To understand this moment, it’s important to understand the role of partisanship and primaries, Butler explained.
‘By opting out of the primaries, people give power to the leaders of the parties to pursue agendas that are not responsive to moderate voters’ preferences.’
Daniel Butler
In today’s highly polarized political environment, most partisans vote along party lines in general elections, even if they are not enthusiastic supporters of the party’s nominee. Because politicians largely vote in line with their party’s agenda, voters know that they will get the same outcome whether the candidate is moderate or more extreme.
“Voters’ reliance on partisanship at the ballot box incentivizes the politicians to largely vote the party position. They don’t have much reason to moderate and reach swing voters or people from the other side,” Butler said. “For majority party incumbents, voting along party lines also is the best option to get things done in the hope of making their party look a little better.”
This also changes the president’s calculation. If people are largely going to vote based on partisanship during the general election, then the president has incentive to try to stack the deck with his most loyal supporters, Butler explained. This is where primaries come in.
“By opting out of the primaries, people give power to the leaders of the parties to pursue agendas that are not responsive to moderate voters’ preferences,” Butler said.
This influence on Congress is not limited to elections. Trump already has shown that he will support primary challengers to Republican incumbents who have defied him, which puts pressure on members of Congress to support the president’s agenda, even when it’s unpopular with general election voters.
As long as disenfranchised Republican voters continue opting out of intraparty contests, Trump will continue shaping the party’s direction — despite low approval ratings and a lack of widespread support for some of his policies — for years to come, Butler said.
Study co-authors include Laurel Harbridge-Yong, a professor of political science at Northwestern University; Hans J.G. Hassell, the LeRoy Collins Professor at Florida State University; and Sarah E. Anderson, interim dean at the Bren School of Environmental Science & Management at University of California, Santa Barbara.
