Independent Vermont Sen. Bernie Sanders called former Clinton strategist James Carville a “political hack” during a Wednesday night appearance on “Anderson Cooper 360.”

The longtime Democratic strategist, who played a key role in former President Bill Clinton’s 1992 victory, told MSNBC’s Joe Scarborough earlier this week that he is “scared to death” at the prospect of Democrats nominating someone like British Labour Party leader Jeremy Corbyn who, like Sanders, is a socialist.

“I’ll say this just as clearly and directly as I can,” Carville said. “The only thing, the only thing between the United States and the abyss is the Democratic Party. That’s it. If we go the way of the British Labour Party, if we nominate Jeremy Corbyn, it’s going to be the end of days … so I’m scared to death.”

Asked by CNN’s Anderson Cooper to respond, Sanders punched back:

“Look, James, in all due respect, is a political hack who said very terrible things when he was working for Clinton against Barack Obama,” said the Vermont senator. “I think he said some of the same things.”

Sanders contended that his movement is “taking on the establishment” before listing off several entities that don’t like him, such as Wall Street and the pharmaceutical industry. (RELATED: ‘Looking Down At People’: Longtime Democratic Strategist Issues Warning To His Party)

“We are taking on Trump, the Republican establishment, Carville and the Democratic establishment,” he said, “but at the end of the day the grassroots movement that we are putting together, of young people, of working people, of people of color, want real change.”