Vermont Sen. Bernie Sanders and former South Bend, Indiana, Mayor Pete Buttigieg got into a heated exchange on the behavior of "Bernie Bros," online supporters of Sanders who have targeted unions and exhibited sexism.

At the beginning of the Nevada debate Wednesday, Buttigieg accused Sanders of wanting to "burn down" the Democratic Party. But Sanders fired back at the candidate, saying he wants to give the working class more influence in government.

"What we are saying, Pete, is maybe its time for the working class of this country to have a little bit of power in Washington rather than your billionaire campaign contributors," he asserted.

Buttigieg took issue with Sanders's statement, saying he's "not the only one who cares about the working class."

"You're the one who is at war with the Culinary Union right here in Las Vegas," said Buttigieg before Sanders interrupted.

"We have the support of unions all across this country," the senator responded.

Buttigieg was referring to incidents where supporters of the Sanders campaign sent threatening messages to Nevada's Culinary Union officials online, over email, and in phone calls.

On Twitter, union officials were called names such as “bitches,” “whore,” “f---ing scab,” and “evil, entitled assholes.” Over email, union officials were referred to as “corrupt mother f---ers” and were threatened that it was “time for people ... to go after you.” Sanders has denounced the behavior and distanced himself from the incidents.

Later on in the debate, Sanders denounced the attacks against members of the Culinary Union. "If there are a few people who make ugly remarks, who attack trade union leaders, I disown those people. They are not part of our movement," he said.

"Our campaign is about issues. It's about fighting for the working families and the middle class. It is not about vicious attacks on other people," Sanders said. "I have a 30-year, 100% pro-union voting record. Do you think I would support, or anybody who supports me, would be attacking union leaders? It's not thinkable."

Buttigieg kept the pressure high on the socialist, questioning his leadership abilities. "It's about how you inspire people to act," Buttigieg said.