Last week on Fox News, Tucker Carlson argued that immigration to the United States would “dilute the political power” of Americans in a segment that also referenced “white replacement theory” — a discriminatory trope, often weaponized by white nationalists, suggesting people of color are “replacing” White Americans.

The segment left the Anti-Defamation League urging Fox News to fire Carlson for his “open-ended endorsement of white supremacist ideology,” the first time the group has made such a demand, according to the Associated Press.

On Sunday, Jonathan A. Greenblatt, chief executive and national director of the ADL, repeated those demands on CNN, slamming Carlson for his remarks and condemning the network’s owners, the Murdoch family, for not immediately taking action.

“I think we’ve really crossed a new threshold when a major news network dismisses this or pretends like it isn’t important,” Greenblatt told to CNN’s Brian Stelter. “This has deadly significance.”

“Tucker has got to go,” he added.

Fox News did not immediately respond to a request for comment on the segment. Last week, a spokeswoman from the network pointed the New York Times toward Carlson’s statements on the show that his argument was about voting rights.

Carlson has often raised ire over his treatment of racism and white supremacy. In 2018, he lost advertisers after he said certain immigrants make “our own country poorer and dirtier and more divided.” In 2019 he claimed white supremacy is a “hoax” and “a conspiracy theory used to divide the country and keep a hold on power.”

The latest incident happened Thursday, when Carlson spoke with Mark Steyn, who was filling in on “Fox News Primetime,” and argued that Democrats are using looser immigration policies to gain votes.

“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. “But they become hysterical because that’s what’s happening actually. Let’s just say it: That’s true.”

Carlson then referenced the racist claim by name, dismissing it as the motivation for his remarks.

“Everyone wants to make a racial issue out of it. Oh, you know, the white replacement theory? No, no, no,” he said. “I have less political power because they are importing a brand new electorate. Why should I sit back and take that?”

The “great replacement theory” was popularized in 2012 by French writer Renaud Camus, who warned that Western countries face an impending White genocide. The phrase has evolved into a bogus notion that a cabal of elite Jews are plotting to replace White populations with immigrants, Muslims and people of color, according to the ADL.

The “theory” has been employed by far-right groups and mass killers. In 2017 hundreds of white nationalists, neo-Nazis and Ku Klux Klan members marched through the streets of Charlottesville, chanting, “Jews will not replace us.” The man responsible for the 2019 massacre in Christchurch, New Zealand, killing 51 people at two mosques, cited the racist claim, as did the gunman who killed 20 people, seven of them Mexicans, at a Walmart in El Paso.

On CNN on Sunday morning, Greenblatt of the ADL said Carlson’s words directly reflect the “replacement theory” and added that it’s not the first time the host has invoked discriminatory ideologies to justify his arguments.

“Tucker Carlson has a history of sanitizing stereotypes and of spreading this kind of poison, but what he did on Thursday night really was indeed, as you put it, a new low,” Greenblatt said.

Greenblatt added that Carlson often makes these claims on a prime-time platform, allowing him to act as a “gateway” to “damaging and dangerous conspiracy theories.”

“There is a reason why people like Richard Spencer or David Duke praise Tucker Carlson,” Greenblatt said, referring to the white nationalist and former KKK leader. “Because indeed he’s taken their talking points and literally used his prime-time platform to mainstream them for millions of Americans.”

The ADL director warned such segments have “real consequences,” noting that the gunman used the racist claim to justify killing 11 worshipers at Tree of Life synagogue in Pittsburgh in 2018.

“So when Tucker Carlson invokes it on his show, when he dismisses it, it is so dangerous,” Greenblatt said.

Greenblatt also took Fox News’s owners to task, accusing them of overlooking the danger because his show brings in the most viewers on the network.

“Where are the Murdochs?” Greenblatt said. “How can they countenance their network being used to mainstream the most violent and toxic ideas?”

Greenblatt suggested advertisers and affiliate stations boycott the show.

“It is incumbent upon … from advertisers, to the cable companies, to the shareholders, to say there is just too much risk in his racism and he’s got to go,” he said.