Rep. Matt Rosendale (R-Mont.) on Friday officially launched his bid for the U.S. Senate, giving Republican voters in Montana a second millionaire transplant to choose from in the upcoming June primary.

Rosendale, a hard-right conservative, will face GOP hopeful Tim Sheehy, a former Navy SEAL and wealthy businessman, for the opportunity to take on incumbent Democratic Sen. Jon Tester in November. Tester, who has held the seat since 2007, is widely considered one of the most vulnerable Democrats up for reelection.

In a video announcement, Rosendale said that he’s running “against the Washington establishment, against [President] Joe Biden and [Senate Minority Leader] Mitch McConnell.” And he touted his loyalty to former President Donald Trump.

Trump endorsed Sheehy hours after Rosendale made his run official.

Rosendale, who unsuccessfully ran against Tester in 2018, has been hinting at a second challenge for months. In a video posted to social media in December, he said that he was “heavily considering” running and slammed McConnell and other Senate Republicans for “propping up” Sheehy and trying to keep him out of the race.

“While it is truly an honor and privilege to represent the people of eastern Montana in Congress, it is difficult for me to stand by and allow Mitch McConnell and the uniparty to sell our country short and attempt to select our next senator,” he said.

Rosendale’s entry into the race sets the stage for a bitter and expensive primary.

Sheehy has the endorsement of several Republican leaders in Washington and at home, including Sen. Steve Daines (R-Mont.), who chairs the powerful National Republican Senatorial Committee, as well as Montana Gov. Greg Gianforte (R), Sen. John Barrasso (R-Wyo.) and Rep. Ryan Zinke (R-Mont.). Rosendale has touted support among state lawmakers in Montana, including Speaker of the Montana House Matt Regier (R).

This week provided a glimpse into how contentious the primary will likely be. Punchbowl News reported early Thursday that U.S. House Speaker Mike Johnson (R-La.) planned to endorse Rosendale in the race. But Johnson reversed course within hours, reportedly after blowback from high-profile Republicans. A spokesperson for Johnson later told CNN that the speaker would donate to but not endorse Rosendale’s campaign.

Zinke, who not long ago was expected to also make a run for Tester’s seat, told Politico on Thursday that “upon reflection, the Speaker withdrew his endorsement largely based on the reality that Rosendale is the weaker candidate by far against Tester.”

Rosendale took to X, formerly Twitter, on Thursday to thank Johnson for his continued support, but at the time stopped short of confirming his Senate candidacy.

“Mitch McConnell and the D.C. Cartel are TERRIFIED about me going to the U.S. Senate,” he wrote. “They know they can’t control me; they know I won’t vote for McConnell as Leader. But they are fixin’ to find out that in Montana, we don’t take orders from Washington; we send orders to Washington!”

Originally from Maryland, Rosendale is a loyal ally of Trump and a member of the ultraconservative House Freedom Caucus. He was among the 147 members of Congress who voted to overturn the results of the 2020 election, and last year joined seven other House Republicans in voting to oust then-Speaker Kevin McCarthy (R-Calif.). Rosendale has a history of mingling with far-right extremists. In 2014, he spoke at a pro-gun Oath Keepers rally in Kalispell, Montana. And last year, he made national headlines when he posed for a photograph outside the U.S. Capitol alongside two well-known white supremacists.

Sheehy is new to politics, likely courted to run because of his military and business acumen and his ability to self-finance his campaign. A Minnesota native, Sheehy moved to Montana in 2014 after retiring from the Navy. He is the founder of Bridger Aerospace, a Bozeman-based aerial firefighting company that relies almost exclusively on federal contracts. While the company has pitched itself as a leader in the fight against climate change, Sheehy has toed the party line on climate while on the campaign trail, railing against what he calls the “climate cult.”

Sheehy’s previous support for addressing climate change will be easy fodder for Rosendale as the primary heats up.

In his December video, Rosendale attacked Sheehy for having “profited off of Biden’s Green New Deal,” an apparent reference to Bridger Aerospace’s reliance on federal contracts.

Rosendale and Sheehy have both endorsed Trump for president in 2024. Trump, who backed Rosendale in 2018 when he ran for Senate and again in 2022 when he was reelected to the House, endorsed Sheehy in a post to his social media platform, Truth Social, on Friday.

Asked about Johnson backpedaling on endorsing Rosendale, Tester, a farmer and lifelong Montana resident, told Politico that it ultimately “doesn’t really matter.”

“It’s the same race either way,” Tester said. “I get to run against an out-of-stater that Mitch McConnell picked or an out-of-stater that Mitch McConnell doesn’t like.”

Montana Democrats had a similar response to news of a Rosendale-Sheehy primary battle.

“Buckle up for the battle of the out-of-staters, because Mitch McConnell and the NRSC’s greatest nightmare in Montana came true,” said Hannah Rehm, a senior communications adviser for the Montana Democratic Party, referring to the National Republican Senatorial Committee.

“Over the coming months, Montanans are going to see how out of touch Maryland Matt and Transplant Tim are with our state.”