From an AP story by Mary Clare Jalonick headlined “GOP senator challenges Teamsters head to a fight in a fiery exchange at a hearing”:

A congressional hearing devolved into an angry confrontation between a senator and a witness on Tuesday after Republican Sen. Markwayne Mullin of Oklahoma challenged Sean O’Brien, the president of the International Brotherhood of Teamsters, to “stand your butt up” and settle longstanding differences right there in the room.

Vermont Sen. Bernie Sanders, the chairman of the Senate panel that was holding the hearing, yelled at Mullin to sit down after he challenged O’Brien to a fight. Mullin had stood up from his seat at the dais and appeared to start taking his ring off.