Rep. Matt Rosendale (R-MT) announced Friday that he will run for Senate in Montana, defying the wishes of national Republicans who hoped to avoid a bitter primary in the must-win state.

Rosendale, a member of the conservative Freedom Caucus, has become a lightning rod for controversy in Congress. He is one of eight Republicans who voted to depose Speaker Kevin McCarthy last year.

But he drew increasing alarm, and anger, as it became apparent he would follow through with an attempted rematch of his 2018 race against the incumbent Democrat, Sen. Jon Tester (D-MT), in November.

Rosendale lost that race by 3 points, fueling concerns from national Republicans over his viability in another general election race. Institutional support has instead gone to Tim Sheehy, a deep-pocketed former Navy SEAL.

Montana, alongside Ohio and West Virginia, is among the most important Senate races this cycle and could very well determine who controls the upper chamber next year.

The choice of Steve Daines (R-MT), Montana’s junior senator, as the chairman of the National Republican Senatorial Committee underscores its perceived importance to party leadership.

Daines is backing Sheehy, as is the McConnell-aligned Senate Leadership Fund, allowing Rosendale to frame his candidacy as an insurgent campaign against the Washington establishment.

“Mitch McConnell and the Uniparty have controlled the Senate for far too long and are the architects of a $34 trillion debt,” Rosendale said in a post on X announcing his campaign. “It’s time they understand that Montanans don’t take orders from Washington, we send orders to Washington!”

Daines, however, framed Rosendale as a chaos agent with a track record of losing.

“It’s unfortunate that rather than building seniority for our great state in the House, Matt is choosing to abandon his seat and create a divisive primary,” he said in a statement. “Whichever party wins the Montana Senate seat will control the United States Senate in 2024, and Republicans cannot risk nominating a candidate who gave Jon Tester the biggest victory of his career.”

Sheehy gave a preview of how divisive that primary could become, posting a video on Friday mocking Rosendale for the way he pronounces Montana. Meanwhile, Tester used his entrance to fundraise for an election that is rated as a “toss-up” by the Cook Political Report.

Beyond party leadership, Rosendale has also received a cold shoulder or outright hostility from former allies. The anti-establishment Club for Growth, despite for months signaling it would support Rosendale, backed away from those plans in July.

The hostility has largely come from Trumpworld, which views Rosendale as disloyal over his decision not to take the former president’s phone call on the House floor as he resisted McCarthy’s ascent to the speakership.

Rosendale also gave what was perceived as a late endorsement for Donald Trump’s 2024 White House run despite him stumping for Rosendale during his 2018 Senate bid.

Those tensions came to a head when the Montana GOP rescinded an invitation for Alex Bruesewitz, a pro-Trump critic of Rosendale, to deliver the keynote address at its winter retreat.

Allies of the former president, including his son Don Jr., viewed the move, first reported by the Washington Examiner, as a slight of Trump himself.

That hasn’t been the only controversy surrounding Rosendale’s Senate run. House Speaker Mike Johnson (R-LA) had considered an endorsement of Rosendale, viewed by some as a way to manage his relationship with a rebellious member of his conference, but quickly faced backlash from within the Montana congressional delegation. Johnson decided against the endorsement on Thursday.

Rosendale does have outspoken supporters in Congress – in particular, Sen. Mike Lee (R-UT) and Rep. Matt Gaetz (R-FL). Gaetz, himself a magnet for controversy, campaigned for Rosendale in Montana in the lead-up to his launch.

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At the state level, the Montana Freedom Caucus had been urging him to run for Senate. But more prominent figures, such as Rep. Ryan Zinke (R-MT) and Gov. Greg Gianforte, have come out in support of Sheehy.

Rosendale timed his announcement to the winter retreat in Montana. On Friday evening, he and Sheehy, who will compete in the June 4 primary, will be special guests at its banquet.