Right-wing Congressman wants to run for Senate in Montana, fueling Republican battle

Mr. Rosendale and Mr. Gaetz were part of the small group of Republicans who unseated Representative Kevin McCarthy as Speaker of the House of Representatives, temporarily halting business in the House. Mr. Rosendale had initially objected to installing Mr. McCarthy in the role because he appeared to reject a House call from Mr. Trump, who had called Ms. Greene to signal his support push.

Mr. Rosendale also has the support of Stephen K. Bannon, the former Trump White House strategist, who is planning a series of campaign events in Montana next month. Mr. Rosendale has been a frequent guest on Mr. Bannon's “War Room” podcast, which is popular with conservatives.

Mr. Rosendale entered 2024 with $1.7 million in his federal campaign account. That's about 40 percent of what he spent on Mr. Tester six years ago, but a tiny fraction of the roughly $44 million that two Republican super PACs have already spent on behalf of Mr. Sheehy, a retired Navy SEAL who founded an aerial firefighting company . .

These groups — the Senate Leadership Fund, which has ties to Sen. Mitch McConnell, the Republican leader, and American Crossroads, co-founded by Karl Rove — have each spent about $22 million on advertising in the state.

A third super PAC supporting Mr. Sheehy, known as More Jobs, Less Government, has been endorsed by a pair of wealthy Wall Street executives. Kenneth Griffin gave $5 million, Paul Singer contributed $1 million and Stephen A. Schwarzman donated $400,000, according to Federal Election Commission filings. The super PAC has hired Tony Fabrizio, Trump's longtime pollster, and Andy Surabian, a strategist who has been involved in all three of Trump's presidential campaigns.

Mr. Tester, meanwhile, has kept pace with the increase in Republican spending. His campaign has spent $5 million on advertising in the state, and has been helped by roughly $50 million in combined spending from WinSenate and Last Best Place, two Democratic super PACs with ties to the Senate Majority PAC, the top group outside the Senate. Democrats.

Maggie Haberman reporting contributed.