Faced with a historically unpopular president and a stalled agenda, a growing number of Republicans in Congress are saying they will not run for re-election in 2018, increasing the odds that Democrats could retake the House in a wave election next year. The latest to withdraw his bid is Michigan Republican Dave Trott, who was facing an uphill battle to re-election in a swing district. Trott joined the ranks of Republicans Ileana Ros-Lehtinen of Florida, Dave Reichert of Washington and Charlie Dent of Pennsylvania—all of whom hail from what are expected to be highly competitive districts in next year’s midterms. John J. Duncan Jr. of Tennessee, Lynn Jenkins of Kansas and Sam Johnson of Texas also announced their retirements earlier this year. And another Michigan Republican, Rep. Fred Upton, may also retire or run for the Senate, according to The New York Times. According to the Cook Political Report, Trott and Reichert’s districts are now toss-ups, while Dent’s previously solid red district has moved into the “Lean Republican” column.

Republicans in vulnerable districts have few good options as they head into 2018. Public sentiment typically turns against the party in control of the White House in midterm elections, and there have rarely been presidents as unpopular as Donald Trump. But as David Drucker reported for Vanity Fair last month, G.O.P. consultants are still advising incumbents and potential candidates to stand by the president. “Your heart tells you that he’s bad for the country. Your head looks at polling data among Republican primary voters and sees how popular he is,” one Republican strategist said. “It would be malpractice not to advise clients to attach themselves to that popularity.”

But standing by the president is exhausting. Even in the Senate, where the G.O.P. is expected to maintain its majority, Republicans are not immune to Trump fatigue. Senator Bob Corker, the chairman of the Foreign Relations Committee, is considering not running for a third term next year, Politico reports. Utah’s Orrin Hatch, the Senate’s oldest member, is also considering retirement, potentially giving a seat to Mitt Romney. Trump himself has suggested that he could endorse primary challengers of Republican senators who have criticized him, like Arizona Senator Jeff Flake and Dean Heller of Nevada.

In the House, the threat mostly comes from Democrats, who experts suggest have a good shot at taking back the lower chamber, especially if Republican defections continue. “I’m afraid that this trickle is going to turn into a flood of moderate Republicans retiring because they don’t want to have to defend Trump and deal with their far right colleagues anymore,” one G.O.P. strategist recently told The Washington Examiner. “It’s got to be exhausting and civilian life looks pretty good.” With Trump’s approval rating hovering around 38 percent, FiveThirtyEight predicts that the G.O.P. would lose the House by 10 points if the election were held today.

Lawmakers in some swing districts could face challenges from both sides. Despite criticism from the Republican establishment, former White House chief strategist Steve Bannon is reportedly ramping up his efforts to recruit potential G.O.P. candidates to unseat incumbents whom he views as disloyal to the president:

The activity has alarmed senior Republicans, who worry it will drain millions of dollars from the party’s coffers to take on Democrats in the general election. [Mitch] McConnell has repeatedly expressed concern to the White House about the danger primaries pose to his members, stressing that it could imperil his narrow four-seat majority, according to three people with direct knowledge of the discussions.

Corker is on Bannon’s hit list, according to Politico, as is Flake, Heller, and Mississippi Senator Roger Wicker. The primary campaign is being coordinated with billionaire G.O.P. donor Bob Mercer, who is reportedly willing to spend millions to punish the president’s enemies. Forced to fend off Trump’s shock troops on the right and potentially unprecedented turnout on the left, it’s no surprise that many Republicans are deciding not to run at all.