Tensions flared on Capitol Hill when a sitting U.S. senator engaged in a heated exchange with a union advocate during a committee hearing on labor issues.

The confrontation escalated to the point where Vermont Sen. Bernie Sanders had to step in as a referee, defusing the situation and preventing the confrontation from becoming physical.

Republican Sen. Markwayne Mullin took the mic to blast Teamsters president Sean O’Brien regarding personal attacks he made against him in June 2023. The labor advocate called Mullin “greedy” and a fraud who fakes like he is “tough.”

O’Brien was at the Tuesday, Nov. 14, hearing, at Sanders’s invitation, to testify to the Senate Health, Education, Labor and Pensions Committee about how unions are improving the lives of working families. Sanders, the committee chairman, might not have been aware of the previous contentious feelings between the union rep and the Oklahoma senator.

Mullin read one of five tweets directly targeting him, reading out loud, “Greedy CEO who pretends like he’s self-made. In reality, it’s just a clown & fraud. Always has been, always will be.”

Greedy CEO who pretends like he’s self made. In reality, just a clown & 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 pic.twitter.com/JNvT7IsA6m

— Sean M. O’Brien (@TeamsterSOB) June 21, 2023

Mullin explained as he read the tweet that he was far from a fraud.

“I wish you was in the truck with me when I was building my plumbing company, myself, and my wife was running the office because I should remember working pretty hard and long hours,” he said.

As he continued to go over the tweet, he landed on the ending: “Quit the tough guy act in these senate hearings. You know where to find me. Anyplace, Anytime cowboy. #LittleManSyndrome.”

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Without skipping a beat, he said, “Sir, this is a time. This is a place. If you want to run your mouth, we can be two consenting adults. We can finish it here if you want to run your mouth. We can be two consenting adults. We can finish it here.”

O’Brien continued to sit at his designated spot as a guest in the hearing and simply said, “OK, that’s fine, perfect.”

“You want to do it now?” the former mixed martial arts fighter-turned-politician said.

“I’d love to do it now,” O’Brien replied, to which Mullin did not hesitate to say, “Then stand your butt up then.”

Instead of standing, O’Brien told him, “You stand your butt up, big guy.”

Just as Mullin hopped on his feet, Sanders, the former presidential candidate and committee chair, intervened, reminding the two men where they were.

“Hold it. No, no, no, sit down. Sit down! You’re a United States senator,” Sanders said as he banged his gavel to establish order. “Sit down, please.”

“This is a hearing. God knows the American people have enough contempt for Congress, let’s not —” Sanders continued but was cut off by Mullin and O’Brien, who tossed potshots at each other.

The back and forth then escalated, with the 46-year-old Mullin challenging O’Brien to a real cage match with the proceeds going to charity.

The elder statesman intervened again, saying, “Excuse me, hold it. Sen. Mullin, I have the mic. If you have questions on any economic issues or anything that was said, go for it. We’re not here to talk about physical abuse.” 

After the hearing, Mullin was firm on his position and did not apologize to the union leader or the public for his conduct.

“He called me out. … He said anytime, anyplace. You don’t call me out and say ‘anytime, anyplace,’ and then not back up what you said, I answered his call. Period,” the GOP rising star said, according to The Hill.

Mullin was also asked if he believed he should be held to a higher standard because he is a member of the Senate.

“I’m still a guy,” the husband and father of six said. “He called me. He said it. I just answered the bell. That was all.”  

Mullin, the first Native American senator in almost two decades and the second Cherokee Nation citizen elected to the Senate boasts a diverse entrepreneurial portfolio with businesses like Mullin Properties, Mullin Farms, Mullin Services, and Mullin Plumbing.

His estimated net worth ranges from $31.6 million to $75.6 million. Notably, he is the sole current serving senator without a bachelor’s degree.