Jonathan Greenblatt, CEO of the Anti-Defamation League, called on Friday morning for the firing of Fox News host Tucker Carlson, after Carlson embraced the white nationalist “replacement” conspiracy theory on Thursday night.

“Now, I know that the left and all the little gatekeepers on Twitter become literally hysterical if you use the term ‘replacement,’ if you suggest that the Democratic Party is trying to replace the current electorate, the voters now casting ballots, with new people, more obedient voters from the Third World,” Carlson said during an appearance on Fox News Primetime. “But they become hysterical because that's what's happening actually. Let's just say it: That's true.”

The so-called “great replacement” theory posits that white people are being systematically “replaced” by people of color through mass immigration. The Guardian explained that under this theory, “replacement has been orchestrated by a shadowy group as part of their grand plan to rule the world … . This group is often overtly identified as being Jews, but sometimes the antisemitism is more implicit.”

The theory has also been linked to far-right terrorists who committed mass shootings in both New Zealand and El Paso, Texas, in 2019. The white nationalist groups who marched in 2017 in Charlottesville, Virginia, were also heard chanting both “You will not replace us” and the variant “Jews will not replace us.”

In addition, Fox News personalities (including Carlson) have promoted the conspiracy theory for years, casting immigration as a “purposeful repopulation of America” and helping to propel the idea further into the mainstream of public discourse.

Carlson’s own escalated rhetoric Thursday night also appeared to tap directly into the calls for direct action that motivated previous attackers. In a twisted logical pirouette, he declared that his opposition to immigration was a “voting rights” issue on the grounds that any new citizens in the country would mean “every time they import a new voter, I become disenfranchised as a current voter.” (Meanwhile, he has also supported conspiracy theories about the 2020 election and the new wave of restrictions on voting rights.)

“Why should I sit back and take that?” he said. “The power that I have as an American guaranteed at birth is one man, one vote, and they are diluting it. No, they are not allowed to do it. Why are we putting up with this?”

Update (4/9/21, 4:30 p.m. EDT): The ADL has sent a letter to Fox News calling for Carlson to be fired, as reported by CNN chief media correspondent Brian Stelter.

“Make no mistake: this is dangerous stuff,” Greenblatt wrote in the letter, addressed to Fox News CEO Suzanne Scott. “The ‘great replacement theory’ is a classic white supremacist trope that undergirds the modern white supremacist movement in America.”