A Montana Republican who mounted a Senate campaign only to be greeted by former President Donald Trump’s near-instant endorsement of his opponent has ended his campaign after just six days.

Rep. Matt Rosendale officially launched a Senate bid last Friday after long teasing his desire for a rematch against Democratic Sen. Jon Tester, whom he lost to in 2018. The news was first reported by Politico.

“I have long been a supporter of the President, and remain so. But I have been forced to calculate what my chances of success would be with Trump supporting my opponent. This race was already going to be tough, as I was fighting against Mitch McConnell and the rest of the Republican establishment in Washington. But I felt like I could beat them, as the voters do not agree with them choosing who would be the next U.S. Senator from Montana,” Rosendale said in a statement.

“However, by my calculations, with Trump endorsing my opponent and the lack of resources, the hill was just too steep.”

Rosendale got an icy reception from national Republicans, who are backing former Navy SEAL and wealthy businessman Tim Sheehy for the GOP nomination.

Trump came out in support of Sheehy mere hours after Rosendale entered the race, establishing that Rosendale wasn’t going to have an easy time. House Speaker Mike Johnson (R-La.) also went back on his rumored plan to endorse Rosendale, a member of the hard-right House Freedom Caucus.

Sheehy, a first-time candidate, has deep pockets and a host of institutional GOP support, including from Sen. Steve Daines of Montana, the chair of the National Republican Senatorial Committee — whom Rosendale claimed, without evidence, attempted to bully him out of running — and Montana Gov. Greg Gianforte.

“Mitch McConnell and the D.C. Cartel are TERRIFIED about me going to the U.S. Senate,” Rosendale posted in a tweet on X last week. “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!”

Sheehy’s backers are eager to avoid a repeat of 2018, when Rosendale lost to Tester by 3.5 percentage points in a state that Trump carried by 24 points two years later.

Sheehy acknowledged Rosendale’s departure in a tweet.

“Matt, Montana is grateful for your service and for showing Washington, D.C. what it means to hold the line on reckless spending. I know working together we’ll win this race and defeat Jon Tester,” he posted.

National Republicans view Montana and Ohio as their two best chances of flipping seats that would give them control of the Senate — and they were eager to avoid an ugly primary that would damage their eventual nominee in the general election.

Another Republican still has until March 11 to enter the race.