A Republican senator and the president of the Teamsters union nearly got in a fistfight Tuesday in the middle of a Senate hearing, until Vermont Sen. Bernie Sanders stepped in and broke it up.

The exchange began when Sen. Markwayne Mullin, Okla., read a tweet that Teamsters President Sean O’Brien had posted in June.

“You want to run your mouth? We can be two consenting adults, we can finish it here,” Mullin said to O’Brien, who was testifying at a hearing on labor unions in America.

“OK, that’s fine, perfect,” O’Brien replied. “I’d love to do it right now.”

“Then stand your butt up then,” Mullin shot back.

“You stand your butt up,” O’Brien said.

Mullin, dressed in a white shirt and no jacket, then stood up and began to move toward O’Brien.

“No, no, sit down! Sit down! You’re a United States senator!” shouted Sen. Bernie Sanders, the Vermont independent and chairman of the Senate Health, Education, Labor, and Pensions Committee

Mullin and O’Brien continued to trash talk each other in the hearing room.

“This is a hearing. And God knows the American people have enough contempt for Congress, let’s not make it worse,” Sanders said.

The feud between the senator and the union boss began months earlier.

Mullin told O’Brien “to shut your mouth” in a heated exchange during a prior hearing in March.

In a social media post later, in June, O’Brien ragged on Mullin as a “clown and a fraud.”

“Quit the tough guy act in these senate hearings. You know where to find me. Anyplace, Anytime cowboy,” O’Brien wrote on X.

Days later, Mullin returned fire, saying he accepted the invitation and proposing a mixed martial arts fight for charity.

It was this exchange that prompted Mullin to challenge O’Brien to a fight in Tuesday’s hearing.

This is developing news. Please check back for updates.