Carlson has faced criticism before for his commentary, including a statement that immigration has made America dirtier. His remarks Tuesday came with the nation rubbed raw by two weekend mass shootings and increased concerns by law enforcement officials about violence attached to white nationalism.
"He has used his platform to push out prejudice," said Jonathan Greenblatt, CEO and national director of the Anti-Defamation League. "I think it's disgusting and I don't think it deserves a place on a major news network."
Fox News Channel representatives did not immediately return messages seeking comment on Wednesday.
Carlson's prime-time show routinely draws more than 3 million viewers on weeknights, second only to Sean Hannity on Fox News. Episodes of his program landed among the Nielsen company's list of Top 20 shows last week for both broadcast and cable television.
On Tuesday, he dismissed the concept of white supremacy as a serious problem for the country.
"The combined membership of every white supremacist organization — would they be able to fit into a college football stadium?" Carlson said. "I mean, seriously. This is a country where the average person is getting poorer, where the suicide rate is spiking."
Adopting a low, mocking voice, he said, "'White supremacy, that's the problem.' This is a hoax, just like the Russia hoax. It's a conspiracy theory used to divide the country and keep a hold on power. That's exactly what's going on."
He said he'd "never met anybody who ascribes to white supremacy. I don't know a single person who thinks this is a good idea. They're making this up. It's a talking point that they can use in this election cycle."
The ADL's Greenblatt said that it was "incredibly irresponsible to even make such a statement while we are still burying people who were gunned down by a white supremacist."
In congressional testimony recently, Michael McGarrity, the FBI's top counterterrorism official, said that his organization was conducting roughly 850 domestic terrorism investigations. White supremacists and other domestic terrorists were being arrested more often, and causing more deaths, than international terrorists, he said.
On Sunday after the shootings in El Paso and Dayton, Ohio, a group of former National Security Council counterterrorism directors issued a statement calling on the government to address domestic terrorism with the same dedication it used to attack international risks following the Sept. 11, 2001 terrorist attacks.
Three of 65 killings committed in the United States in 2016 by people associated with bigoted or extremist ideologies were by white supremacists or the far right, according to the Center for the Study of Hate and Extremism at Cal State-San Bernardino. Last year, 17 of 22 such killings involved white supremacists or the far right. The numbers will be higher this year, the center said.
"I don't know what the heck Tucker Carlson is talking about," said Brian Levin, the center's executive director. "This kind of drivel ends up infecting the socio-political discourse with perspectives that are simply not supported by the facts."
Carlson need only have listened to his own network for a different view. Fox News White House correspondent John Roberts, reporting after Trump's Monday speech about the shootings, noted that there were seven mass shootings by white extremists in the past 18 months.
"There are a lot of people out there who will tell you ... that white nationalism, white extremism is a growing threat to this country and perhaps an underreported threat," Roberts said.
Carlson received a tweet of support Wednesday from former Ku Klux Klan leader David Duke, who wrote that "Tucker is RIGHT!"
"Millions of white activists are NOT 'supremacists,'" Duke wrote. "We seek NOT to oppress or destroy any race! Human rights for all — EVEN FOR WHITE PEOPLE! Stop antiWhite racism!"
Carlson is a prominent conservative activist who worked at both CNN and MSNBC and started the web site The Daily Caller. His profile increased when he replaced Bill O'Reilly in Fox's prime-time lineup in 2017.
Some of his comments have provoked advertiser boycotts, like when he said last December that immigration made the country "poorer, dirtier and more divided." He's publicly questioned the notion of whether diversity makes the nation stronger and said Minnesota Rep. Ilhan Omar "is living proof that the way we practice immigration has become dangerous to this country."
Associated Press writer Michael Kunzelman in College Park, Maryland, and researcher Rhonda Shafner in New York contributed to this report.