The Republican push to flip a Democrat-held House seat in a swing district that President Donald Trump carried in his three White House runs just got a big boost.

Hours after four-term House Democratic Rep. Jared Golden announced that he wouldn’t seek re-election in the 2026 midterms in Maine’s 2nd Congressional District, two top nonpartisan political handicappers shifted the now open seat towards the Republicans.

The race in the district, which is the second-most rural in the U.S. and the largest east of the Mississippi River, is one of the most closely watched House contests in the country next year as the Republicans aim to hold their fragile majority in the chamber. And Golden’s announcement rocked the race.

“I’ve been fielding calls for the last 24 hours about how this is a bellwether for whether or not the Democrats can try to retake Congress, as this was, by many accounts, the most competitive House seat in the nation,” veteran Republican consultant Brent Littlefield told Fox News Digital on Thursday.

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Littlefield is the top campaign advisor to former two-term GOP Gov. Paul LePage, who earlier this year decided to come out of political retirement and launch a congressional bid in the district.

Golden, a U.S. Marine veteran who deployed to the wars in Afghanistan and Iraq, and who often bucks his own party in Congress, has held the seat since first winning it in 2018. He won re-election last year by a razor-thin margin.

“After 11 years as a legislator, I have grown tired of the increasing incivility and plain nastiness that are now common from some elements of our American community — behavior that, too often, our political leaders exhibit themselves,” Golden said in an op-ed for the Bangor Daily News, where he revealed his unexpected decision.

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The moderate Democrat took shots at both parties in his 2026 announcement.

“We have seen mainstream Republicans stand by as their party was hijacked first by Tea Party obstructionists and then by the MAGA movement and its willingness to hand much of Congress’ authority to the president,” Golden wrote.

And he added, “I fear Democrats are going down the same path. We’re allowing the most extreme, pugilistic elements of our party to call the shots.”

In the wake of Golden’s announcement, nonpartisan political handicapper Inside Elections said, “we’re changing our rating from Tilt Democratic to Likely Republican, in a positive development for the GOP and making it more challenging for Democrats to gain the three seats they need for a majority.”

And Sabato’s Crystal Ball, another leading nonpartisan handicapper, shifted the race from toss-up to lean Republican.

“Republicans will flip this seat red in 2026,” National Republican Congressional Committee (NRCC) spokeswoman Maureen O’Toole pledged.

But Rep. Suzan DelBene, the chair of the rival Democratic Congressional Campaign Committee (DCCC), emphasized that “Democrats will do everything necessary to keep this seat blue so that Mainers continue to have a voice fighting for them in Congress — and we are confident we will be successful.”

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Golden had been facing a primary challenge from longtime politician and current state auditor Matt Dunlap.

“In the days and months ahead, I intend to vigorously campaign for Congress in Maine’s second congressional district – and I intend to win,” Dunlap vowed on Wednesday.

But sources told Fox News Digital that the DCCC is now recruiting for another candidate in the race.

Golden wrote in his op-ed, “I don’t fear losing. What has become apparent to me is that I now dread the prospect of winning. Simply put, what I could accomplish in this increasingly unproductive Congress pales in comparison to what I could do in that time as a husband, a father and a son.”

LePage, in a social media post Wednesday afternoon, didn’t directly mention Golden but wrote, “This race has always been about fighting for rural Maine. As Governor, I spent eight years helping create jobs and making Maine more prosperous. I am running for Congress to make sure that working Maine families have a voice in Washington D.C. This fight is just beginning.”

But on Thursday, the 77-year-old LePage posted to social media a recent poll that indicated he held a 5-point lead over Golden in next year’s showdown, adding that “LePage wins in every poll.”

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LePage then juxtaposed the news that Golden wouldn’t seek re-election.

But Littlefield isn’t taking anything for granted, especially after this week’s convincing election victories by Democrats in high-profile contests in blue-leaning New Jersey and Virginia.

“It’s still going to be a tough race,” Littlefield told Fox News Digital. “It’s not a cakewalk.”

Fox News’ Liz Elkind contributed to this report