Rep. Fred Upton, R-Mich., is running for re-election in 2018, and will drop his plans to run for Senate.

The surprise move is a boost for House Republicans, who have endured a string of retirements as many fear being swept out of office next year in a midterm wave, and some feel alienated in a party that is tilting toward President Trump's populism. Upton's decision stems a tide of recent bad news for the party, especially after an off-year wipeout in suburban strongholds from Virginia to New York signaled trouble ahead.

“I will not be a candidate for the U.S. Senate. There was a path, but today we are choosing not to follow it," Upton said in a statement shared with the Washington Examiner. “Instead, my focus will remain on helping all of my constituents with problems big and small and improving the quality of life for all in Michigan."

Upton's decision puts House Republicans in a better position to defend Michigan's competitive 6th Congressional District, a perennial Democratic target.

Still, Trump's low polling numbers and retirements in swing districts threaten the GOP's hold on the House majority. On their way out are Reps. Charlie Dent, R-Pa.; Dave Reichert, R-Wash.; and Pat Tiberi, R-Ohio. Also, Republican Rep. Martha McSally is expected to announce her retirement early next year so that she can run for Senate in Arizona.

The gloom has affected Republicans in the Senate as well, as Sens. Bob Corker, R-Tenn.; and Jeff Flake, R-Ariz., have announced their retirements.

Upton, 64 and in the House since 1987, had actively considered challenging Sen. Debbie Stabenow, D-Mich. He had to weigh the value of serving in a polarized House without the House Energy and Commerce Committee gavel he was forced to relinquish because of term limits, as well as the viability of holding a swing seat in the Trump era.

Initially hot on the Senate race and convinced there was a path to the Republican nomination, Upton lately faced new polls showing he could face an uphill battle. Republican voters in the state prefer political outsiders, like Trump, who narrowly won Michigan last year, and that is a quality Upton, a thoughtful and effective legislator, could not offer — in either style or substance. Upton chose to stick around.

"We need focus and fortitude in Washington now more than ever. We are full speed ahead for re-election in 2018," he said.

Upton's announcement could trigger movement in the Senate campaign. John James, a businessman and military veteran, and retired judge Bob Young are examples of people who have garnered early buzz and endorsements.