CNN host Anderson Cooper pushed back against Massachusetts Sen. Elizabeth Warren (D), who supported Democratic presidential candidate Hillary Clinton during the election, for labeling one of President-elect Donald Trump's top advisers a "white supremacist."

The clash came when Warren accused controversial Trump campaign CEO Steve Bannon, a former Breitbart executive soon to be the president-elect's chief strategist, of being a racist.

"[Trump’s] got as his strategic adviser someone who's a white supremacist," she said of Bannon during an interview on CNN's "Anderson Cooper 360º."

But Cooper quickly interjected: "Wait a minute, there’s no evidence he’s a white supremacist. Obviously, there are people who are white supremacists who support Donald Trump and support Breitbart or Steve Bannon."

"There's no evidence he's a white supremacist" @andersoncooper challenges @SenWarren's charge against @StephenBannon https://t.co/1HZJ1jhjMz

— Anderson Cooper 360° (@AC360) December 1, 2016

Warren, clearly frustrated by Cooper's challenge, began rolling her eyes and exhaling at the suggestion that it has not, in fact, been proven that Bannon is a "white supremacist."

"Come on," she grumbled. "Steve Bannon has certainly associated himself with white supremacists — will you go that far?"

The CNN anchor again told Warren he's not certain it's fair to just accuse Bannon of practicing racist ideologies.

"This is a guy whose appointment is applauded by the [Ku Klux Klan]," Warren retorted. "He’s associated himself with white supremacists. Is that close enough?"

"What Donald Trump is doing — so far — is that he’s said he’s going to go forward on bigotry and he’s going to go forward on Wall Street insiders," she continued. "I think this is a real problem for the American people."

The accusation that Bannon is a "white supremacist" stems largely from his work with Breitbart News, a website that is certainly friendly to the so-called "alt-right," which, while not innately a white nationalist faction of right-wing politics, has certainly been a comfortable home for those who subscribe to a white supremacist worldview.

Trump, for his part, told the New York Times last week that he would never have hired Bannon "if I thought he was a racist or alt-right or any of the things, the terms we could use."