Tensions are running high at a Congressional hearing including union leaders. Oklahoma Republican Senator Markwayne Mullin stood up in an apparent move to physically fight Teamsters President Sean O' Brien during the hearing this afternoon. The move came after O'Brien challenged Mullin to a fight in June on Twitter, calling the lawmaker a "clown" and "fraud." Mullin used his time during questioning to confront O'Brien over the comments before eventually challenging him to a fight. Senator Bernie Sanders intervened, telling Mullin to sit down and act like a senator.