A conservative firebrand has officially filed to run for the Montana Senate in the heated contest to unseat Democrat Sen. Jon Tester.

Rep. Matt Rosendale, R-Mont., made the long awaited announcement Friday on X, formerly known as Twitter. 

"We’ve made great accomplishments in the House, only to see them die at the hands of Mitch McConnell and Chuck Schumer in the Senate," he wrote in a post.

Rosendale's bid stirs up the state's Republican primary race, where he will be challenging former Navy SEAL Tim Sheehy for the nomination. 

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When asked about a potential primary challenger earlier this week, Sheehy told Fox News Digital that he is "focused on Jon Tester."

"I'm focused on gaining control of the Senate for conservatives, so we can return common sense policy to D.C," Sheehy said. "We have to reform both parties. We've got a dysfunctional Congress right now in both houses. We need a new generation of leadership in both houses, and it's about time we start getting things done."

However, Sheehy didn't waste time taking a shot at Rosendale Friday morning, posting a video compilation of him pronouncing Montana and saying that he "can't say Montana right."

Sheehy, a first-time candidate, has already gained endorsements from Sen. Steve Daines, R-Mont., Rep. Ryan Zinke, R-Mont., and Gov. Greg Gianforte. 

Daines reaffirmed his endorsement of Sheehy, writing that Rosendale's Senate run could "create a divisive primary."

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"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. Tim Sheehy has my full support because he is the best candidate to take on Jon Tester," Daines wrote in a statement after the announcement. "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."