An Oklahoma senator and a union boss squared off in a congressional hearing on Tuesday, each daring the other to “stand your butt up” and fight in an exchange the chair of the Senate labor committee, Bernie Sanders, struggled to contain.

“Sit down!” Sanders shouted at Markwayne Mullin, the Republican on the dais beside him. “You’re a United States senator!”

Mullin, 46, called Sean O’Brien, president of the Teamsters union, a “thug”.

O’Brien, 51, said Mullin was acting like “a schoolyard bully”.

Sanders, 82, banged his gavel in vain.

The face-off began when Mullin read out a tweet O’Brien sent earlier this year, after another committee-room confrontation.

In the tweet, O’Brien called Mullin a “greedy [chief executive] who pretends like he’s self-made. In reality, just a clown and fraud. Always has been, always will be. Quit the tough guy act in these Senate hearings. You know where to find me. Anyplace, Anytime cowboy. #LittleManSyndrome.”

Before entering Congress, Mullin made his money in plumbing. He is also a former cage fighter who in 2021 had to reassure voters he did not think he was Rambo, after trying to enter Afghanistan during the US withdrawal.

In his initial response to O’Brien’s tweet, Mullin offered to fight him for charity. In Tuesday’s hearing, Mullin finished reading the tweet, then told O’Brien: “You want to run your mouth? We can be two consenting adults, we can finish it here.”

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

Mullin said: “Then stand your butt up then.”

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

Mullin stood his butt up – and began to advance.

Sanders took action, shouting: “No, no, sit down! Sit down! You’re a United States senator!”

Mullin sat down.

The two men continued to squabble, Sanders banging his gavel.

O’Brien said: “Can I respond?”

Sanders said: “No, you can’t. This is a hearing. And God knows the American people have enough contempt for Congress, let’s not make it worse.”

Elsewhere on Capitol Hill on Tuesday a Republican congressman from Tennessee, Tim Burchett, took “a clean shot to the kidneys” from the speaker he helped eject last month, Kevin McCarthy of California, as a reporter watched.

The Senate labor committee hearing continued to descend into disorder, Mullin saying: “I don’t like thugs and bullies.”

O’Brien said: “I don’t like you, because you just described yourself.”

Sanders banged his gavel again, cueing Mullin to speak.

“All right,” Mullin said. “Let’s do this because I did challenge you and I accepted your challenge. And you went quiet.”

O’Brien said: “I didn’t go quiet. You challenged me to a cage match, acting like a 12-year-old schoolyard bully.”

Sanders intervened again.

“If you have questions on any economic issues, anything, go for it,” he said. “We’re not here to talk about physical abuse.”

Mullin said he wanted “to expose this thug for who he is”.

O’Brien said: “Do not point at me, that’s disrespectful.”

Mullin said: “I don’t care about respecting you at all.”

O’Brien said: “I don’t respect you at all.”

Shouting, “Hold it, no,” Sanders banged his hammer again.

Outside, public approval ratings for Congress and its members continued their downward march.

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