Weeks before Election Day, President Trump is stepping in to help stop a Republican from winning in Colorado.

For months, commentators and political strategists have praised the state’s Republican nominee for U.S. Senate, businessman Joe O’Dea, as one one of the best candidates that the party put forward this year, even if he was an underdog.

Now, Mr. Trump is taking to Truth Social to throw his own party’s candidate under the bus, calling Mr. O’Dea a Republican in name only, and attacking him for saying “he wants to ‘distance’ himself from” the former president.

“He should look at the Economy, Inflation, Energy Independence, defeating ISIS, the Strongest EVER Border, Great Trade Deals, and much more, before he speaks. MAGA doesn’t Vote for stupid people with big mouths. Good luck Joe,” the president wrote.

For GOP leaders, Mr. Trump’s tirade is sure to dredge up painful memories of the 2021 Senate runoffs in Georgia. Mr. Trump is widely blamed for the Republicans losing both of those seats due to his attacks on the integrity of the election. Losing the seats cost the GOP control of the Senate.

In response to the president’s broadside, Mr. O’Dea said Mr. Trump is entitled to his opinion, but “I’m my own man and I’ll call it like I see it.”

“Another Biden-Trump election will tear this country apart,” he added. “DeSantis, Scott, Pompeo, or Haley would be better choices. These elections should be focused on Joe Biden’s failures — supercharged inflation, a broken border, rampant crime, a war on American energy — not rehash of 2020. America needs to move forward.”

Mr. Trump’s new comments come only a day after Mr. O’Dea told CNN that he would campaign against Mr. Trump if the former president were to run again in 2024.

“So if Donald Trump should run again, I’m going to actively campaign against Donald Trump and make sure that we’ve got four or five really great Republicans right now,” he said.

Mr. O’Dea went on to name Governors DeSantis and Haley and a U.S. senator of South Carolina, Tim Scott, as potential Republican candidates for president in 2024, after criticizing Mr. Trump for his lack of action to stop the events of January 6, 2021.

The interview on CNN was an escalation of Mr. O’Dea’s public break with Mr. Trump, from whom he has previously said that “the country is ready to move on.”

Mr. O’Dea has also tried to separate himself from the Republican establishment, casting himself as a “Republican Joe Manchin,” referring to the U.S. senator of West Virginia, though his comments have not drawn public response from party leaders. 

“They’re not going to know where Joe O’Dea’s at,” Mr. O’Dea said at a Denver Chamber of Commerce candidate forum. “I’ll buck the party. If [Senator] McConnell wants my vote, we’re going to get good things done for Colorado. I’ll sit there and I’ll just wait him out. I don’t care.”

Colorado had been pegged as one of the GOP’s best pickup opportunities by the president of the National Republican Senatorial Committee, Senator Scott of Florida.

“I’m 100% certain we’ll take the Senate,” he said to Gray Television late last month. “I think we’ve got a great opportunity in Arizona, Colorado, Washington, New Hampshire. So I think we’re going to have a breakthrough.”

Mr. O’Dea’s collision course with Mr. Trump began when he defeated Trump-backed candidates in the GOP primary in Colorado, largely because he was able to win over independent voters who are allowed to vote in the state’s party primaries.

In the primary, Democrats attempted to prop up Mr. O’Dea’s opponents, hoping that GOP voters would nominate one of the more extreme candidates.

His perceived moderation and ability to win over independents has helped him stand out from a crowd of lackluster, mostly Trump-backed Republican Senate candidates this year.

Mr. O’Dea managed to invoke Mr. Trump’s wrath as his campaign, alongside many other Republican campaigns, was picking up steam in the run-up to November 8.

An October 6, Marist poll found that Mr. O’Dea has closed some of his deficit against the Democratic incumbent, Michael Bennet. The poll suggested that Mr. Bennet’s earlier, double-digit lead over Mr. O’Dea has shrunk to 6 points.

Although Mr. O’Dea trails Mr. Bennet in the polls, the director of the Marist Institute for Public Opinion, Lee Miringoff, did note that the candidates are “neck-and-neck” among independents, who helped propel Mr. O’Dea to the nomination.