When President-elect Joe Biden takes office on Jan. 20, he’ll face very narrow majorities in both chambers of Congress. Depending on who wins the runoff elections for Georgia’s Senate seats, Democrats will either have slim majorities in both houses of Congress or the parties will split control of the House and Senate. Either way, lawmakers will have to compromise to pass legislation on pressing issues such as the pandemic and the associated economic crisis, climate change, racial justice and immigration.

Many argue that partisan disagreements between Democrats and Republicans limit the prospects for bipartisan dealmaking. But there’s another possible roadblock. As our new research shows, legislators often reject compromise because they believe it puts their reelection at risk.

Here’s how we did our research

In our new book “Rejecting Compromise: Legislators’ Fear of Primary Voters,” we investigated whether legislators believe that compromise is electorally risky. Because it is difficult to survey members of Congress, we turned instead to state legislators, probing their willingness to compromise across a host of prominent issues.

In 2014, we emailed a survey to all state legislators and had a 5 percent response rate. The 257 legislators who responded were representative of the full population of state legislators in terms of their gender and majority status in the legislature. And while Democrats were more likely to respond, 43 percent of the sample were Republicans.

Among the legislators who responded, nearly a quarter said they’d vote against a compromise gas tax proposal that would move the existing state gas tax halfway toward the level of taxation they prefer. Legislators from both political parties rejected this half-a-loaf compromise.

We can observe such behavior in action. Lawmakers in both Congress and state legislatures frequently reject compromises that give them some but not all of what they seek. On the issue of health care, for example, some Republicans opposed “Obamacare Lite” that would have rolled back some though not all of the Affordable Care Act. And on energy issues, some Democrats in California voted against reauthorizing a state cap-and-trade climate program because they thought it wasn’t strong enough.

We followed up our initial survey with another one that we distributed at the 2017 National Conference of State Legislatures’ Annual Legislative Summit in Boston. The 215 legislators who took the survey came from 44 different states and both parties, with one-third of them Republicans and two-thirds Democrats. We asked these lawmakers how donors, primary voters and general election voters would respond if they supported a compromise without giving any specifics of the compromise.

Lawmakers fear primary voters the most

In our second survey, we learned that many legislators reject policy compromises because they fear that voters will punish them in their next primary election. Over half of legislators (58 percent) said that they thought voters in their party’s primary election would be either somewhat or very likely to punish them if they compromised. Legislators held very different views about general election voters. Only a quarter of legislators thought general election voters would be somewhat or very likely to punish them. What’s more, they feared that primary voters would be more likely to punish them than would campaign donors — even though many observers, including scholars, former members of Congress, and President Barack Obama, often blame donors for Congress’s inability to solve important problems. Only 40 percent of legislators thought campaign donors would punish them for compromising.

When we asked open-ended questions, many legislators’ comments reinforced this. When asked whether they could name a time someone lost a seat because of a legislative compromise, one attendee wrote that it would happen “in a contested primary, not a general election.” Another put it even more bluntly: “In my state primary voters are probably the biggest deterrent to legislative compromise.”

Fear of punishment may be even higher in U.S. congressional elections, where a legislator’s voting record is more likely to make the news or be advertised by relevant interest groups.

This fear affects all legislators, not just those who have actually faced primary challenges. Savvy legislators anticipate what voters want and avoid supporting compromises that they think will alienate their primary voters.

What that means for 2021 and beyond

Legislators are already looking forward to the primaries that begin little more than a year after Biden takes office. The latest round of primaries gave them little reason to relax; in 2020, many long-serving incumbents faced primary challengers who argued that the incumbents were too moderate for the district.

This trend has been accelerating for decade. In 2012, Sen. Richard G. Lugar (R-Ind.) lost to a primary challenger; so did Rep. Eric Cantor (R-Va.) in 2014. In both cases, opponents argued the incumbents were too willing to compromise — as happened again to longtime incumbents this year. As Rep. Ro Khanna (D-Calif.) argued this past September, “Progressives have to stand for certain basic values: reproductive choice, LGBT equality, the rights for Dreamers. These things should not be places where we compromise.”

On the Republican side, Denver Riggleman (Va.) and Scott R. Tipton (Colo.) lost to conservative challengers; in Democratic primaries, William Lacy Clay (D-Mo.), Daniel Lipinski (D-Ill.) and Eliot L. Engel (D-N.Y.) lost to more progressive challengers. Lipinski often emphasized the need for compromise and pragmatism, saying, “Compromise has become a dirty word in Washington.”

In a world of pressing problems, incumbents’ fear of primary voters helps stymie compromise solutions.

Sarah E. Anderson (@Prof_SEAnderson) is a professor of environmental politics at the University of California at Santa Barbara.

Daniel Butler is a professor of political science at the University of California at San Diego.

Laurel Harbridge-Yong is an associate professor of political science and a faculty fellow at the Institute for Policy Research (@IPRatNU) at Northwestern University.