Sean O’Brien, head of the International Brotherhood of Teamsters, was serving as a witness before the Senate Health, Education, Labor and Pensions Committee on Tuesday for a hearing focused on how labor unions are improving the lives of working families. 

But the hearing took a turn when Mullin, after reading aloud the union leader’s tweets calling the senator a “clown” and a “fraud,” challenged O’Brien to a fight on the spot.

“Sir, this is a time, this is a place. You want to run your mouth, we can be two consenting adults, we can finish it here,” Mullin said from the hearing room dais.  

“OK, that’s fine. Perfect,” O’Brien shot back.  

“You want to do it now?” Mullin, a former mixed martial arts fighter, asked. “Stand your butt up then.”  

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

Mullin, who is 46 years old, stood as if he was preparing to spring into the middle of the hearing room to trade blows with the Teamster. 

At that point, Sen. Bernie Sanders (I-Vt.), who heads the committee, tried to take control of the hearing.

“Hold it. No, no, no, sit down. Sit down! You’re a United States senator, sit down,” Sanders yelled while banging the gavel to restore order in the room. 

The back and forth marked the latest clash between Mullin and O’Brien.

The pair feuded at a March hearing when O’Brien called Mullin, who previously owned a plumbing company, a “greedy CEO,” and Mullin told the union official to “shut his mouth.” 

The Hill’s Alex Bolton has the details here.