President Trump on Wednesday renewed his attacks on CNN’s Don Lemon, one of the moderators of the Democratic debate, calling him “the dumbest man on television” and suggesting he was “too dumb” to understand that he should ask fair questions.

Trump’s ire, directed at an African American TV host whose intelligence he has publicly questioned before, appeared prompted by Lemon’s assertion at Tuesday’s debate in Detroit that Trump is pursuing “a reelection strategy based in part on racial division.”

Lemon’s questioning of the Democratic candidates came in the wake of relentless attacks in recent weeks by Trump on House Oversight Committee Chairman Elijah E. Cummings (D-Md.), an African American, and four liberal minority congresswomen known on Capitol Hill as “the Squad.”

“CNN’s Don Lemon, the dumbest man on television, insinuated last night while asking a debate ‘question’ that I was a racist, when in fact I am ‘the least racist person in the world,’ ” Trump wrote on Twitter. “Perhaps someone should explain to Don that he is supposed to be neutral, unbiased & fair, or is he too dumb (stupid} to understand that.”

Trump, who frequently accuses CNN of biased coverage, added: “No wonder that CNN’s ratings (MSNBC’s also) have gone down the tubes - and will stay there until they bring credibility back to the newsroom. Don’t hold your breath!”

While questioning former Texas congressman Beto O’Rourke during Tuesday’s debate, Lemon stated that Trump “is pursuing a reelection strategy based in part on racial division.”

“How do you convince primary voters that you’d be the best nominee to take on President Trump and heal the racial divide in America?” Lemon asked.

He later asked Sen. Amy Klobuchar (D-Minn.), “What do you say to those Trump voters who prioritize the economy over the president’s bigotry?”

After Trump’s tweet Wednesday, O’Rourke responded on Twitter, writing “Donald Trump is a racist” and sharing footage of his own response to Lemon.

Lemon, one of three moderators Tuesday night, has been among CNN’s most outspoken critics of Trump, especially on issues of race, making him one of Trump’s frequent media foils.

While a Republican presidential candidate in August 2016, Trump described Lemon on Twitter as “dumb as a rock” after he critically covered an episode in which Trump said “Second Amendment people” could take matters into their own hands if Hillary Clinton is elected president and appointed judges who favored stricter gun-control measures.

Two years later, Trump tweeted that Lemon was “the dumbest man on television.”

After that attack, Lemon devoted a segment on his prime-time CNN show to condemn Trump’s name-calling.

“Some of those people are white,” Lemon said, referring to Trump’s targets. “But I would just like to note that referring to an African American as dumb — remember, this is America — is one of the oldest canards of America’s racist past and present, that black people are of inferior intelligence.”

In January 2018, after reports that Trump had referred to African nations as “shithole countries,” Lemon opened his show this way: “This is ‘CNN Tonight.’ I’m Don Lemon. The president of the United States is racist. A lot of us already knew that.”

Friction between the two men dates to a 2011 interview, when Trump, then a real estate mogul and television reality-show star, was considering a run for president and was promoting the false birther conspiracy theory that President Barack Obama was born in Kenya.

When Lemon pushed Trump on the issue, Trump said: “I want to tell you I am the least racist. I am a wonderful person as far as you would be concerned as to race.”

Lemon has claimed that after the interview ended, Trump vowed to never appear on his show again, suggesting because Lemon is black, he could not be unbiased.

Despite his antipathy, Trump apparently sometimes watches the show.

In August of last year, he weighed in on Twitter after Lemon interviewed basketball star LeBron James on his show.

“Lebron James was just interviewed by the dumbest man on television, Don Lemon,” Trump wrote. “He made Lebron look smart, which isn’t easy to do.”

As of Wednesday, Lemon had pinned a tweet referencing the episode to the top of his Twitter feed. It included a video of James discussing his charitable efforts aimed at at-risk students.

“Who’s the real dummy? A man who puts kids in classrooms or one who puts kids in cages?” Lemon wrote, referencing conditions at migrant detention facilities run by the Trump administration.

In recent days, Trump has repeatedly attacked Cummings, a powerful African American lawmaker, and Baltimore, the city he represents. Trump has called Baltimore a “rodent infested mess” and claimed that Cummings is a “bully” who has done nothing to improve conditions in the city.

Earlier this month, Trump repeatedly attacked Reps. Alexandria Ocasio-Cortez (D-N.Y.), Ilhan Omar (D-Minn.), Ayanna Pressley (D-Mass.) and Rashida Tlaib (D-Mich.). In an initial tweet, he said the four minority congresswomen should “go back” to the “totally broken and crime infested places from which they came.”

Only Omar, a Somali refu­gee, was born outside the country. She became a U.S. citizen in 2000.