Almost nothing could stop Rep. Matt Rosendale (R-MT) from running for Senate in Montana.

Party leaders pleaded with him to sit the race out, while anti-establishment heavyweights like the Club for Growth pulled back support.

Republicans were wary from his last Senate bid. In 2018, he lost to Sen. Jon Tester, the current Democratic incumbent, by 3 points.

But Rosendale decided past is not prologue and charged forward anyway. On Feb. 9, he entered the race with a defiant video declaring he would take on the Washington establishment.

Six days later, he dropped out.

The decision marked a dramatic and consequential reversal. Republicans were bracing for a deeply divisive primary in perhaps the most important state on the Senate map. Now, they have a clear path.

However, it also put a finer point on what had been in question: Donald Trump’s control over the GOP.

On the same day that Rosendale announced his candidacy, the former president endorsed Tim Sheehy, his primary opponent.

Rosendale pitched himself as a MAGA warrior, but he lost out due to his perceived disloyalty to Trump.

His original sin? A decision not to take Trump’s phone call on the House floor during the Kevin McCarthy speaker’s race.

Rosendale understood the “tough” fight he faced with national Republicans lining up against him — “I felt like I could beat them,” he said in a statement bowing out of the race — but it took Trump weighing in to dissuade him.

“With Trump endorsing my opponent and the lack of resources, the hill was just too steep,” he said.

The calculation was not altogether surprising. Montana is Trump Country, and his endorsement carries weight.

But it underscored Trump’s continued, and sometimes singular, ability to make or break a career in Republican politics.

His command of the GOP came into doubt following the midterm elections. In pivotal races, he endorsed candidates only for them to lose in the general election.

He even appeared weak enough that a dozen Republicans challenged him for the presidency in 2024.

Yet Trump’s insurmountable lead in the polls, buoyed by the criminal indictments against him, led most to drop out.

The only challenger left is former U.N. Ambassador Nikki Haley, who trails the former president by more than 30 points in her home state of South Carolina, days before a pivotal primary there.

Whether Trump will hurt Republicans in November is once again an open question. The party has a favorable Senate map to begin with, and the states that will be decisive — Ohio, Montana, and West Virginia — were all won by Trump in 2020.

His impact on the House majority is less clear.

Democrats have used his sway over the party to paint even centrists as “MAGA extremists.” But in red states and districts, a Trump endorsement reigns supreme.

Some candidates have lobbied harder for it than others.

In Ohio, Senate hopeful Bernie Moreno earned Trump’s support in part through his full-throated insistence that the 2020 election was stolen.

His rival Frank LaRose, meanwhile, struggled to embrace Trump fully yet still vied for his backing. In August, he fired a staffer over tweets critical of the former president. 

“Donald Trump is the kingmaker of the Republican Party. He has dominated the GOP field in the presidential primary, but also cleared the field for Senate candidates like Kari Lake and Tim Sheehy,” said one Republican strategist.

Sen. Steve Daines (R-MT), the chairman of the National Republican Senatorial Committee, clearly recognizes Trump’s influence. He has worked closely with the former president to avoid costly primaries, to greater and lesser success.

Lake, endorsed by Trump and Daines for the Arizona Senate seat, only faces a nominal primary challenge from Pinal County Sheriff Mark Lamb after 2022 candidate Blake Masters flirted with and then passed on a challenge himself.

But Montana is the shining example. 

“I appreciate Matt’s many years of service to Montana. It will take all Republicans working together to defeat Jon Tester in November,” Daines said in a statement after Rosendale dropped out.

The level of coordination with Trump is in some sense stunning. The former president has gone from political outsider to head of the party establishment in a handful of years.

If that wasn’t clear during his presidency, it certainly is now.

The realignment is easier for Daines, one of the more conservative members of Senate Republican leadership. But even Trump’s biggest GOP foe, Senate Minority Leader Mitch McConnell (R-KY), has found common ground with him in states such as West Virginia.

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Trump has exerted his influence in other ways. He has called for new leadership at the Republican National Committee, attempting to install his daughter-in-law as co-chairwoman.

But his dominance is neatly illustrated in Haley’s attempt to frame herself as the outsider as she makes what could be her final stand in South Carolina.