Piers Morgan, a British TV host and one of President Trump’s most vocal supporters, issued a scathing column Thursday saying the “send her back” chant at his rally in North Carolina was the “most sickening moment” of his presidency.

Mr. Morgan, writing for The Daily Mail, said the people gathered Wednesday night in support of Mr. Trump’s reelection campaign “seemed united in racist rage” when they chanted “send her back,” referring to Democratic Rep. Ilhan Omar, a U.S. citizen who immigrated from Somalia as a child.

“Vile. Repellent. Shameful. Shocking. Disturbing,” Mr. Morgan wrote. “Those were my first thoughts as I watched the crowd at President Trump’s rally in North Carolina last night frenziedly chanting ‘SEND HER BACK! SEND HER BACK!’ about Muslim US congresswoman Ilhan Omar — as their President stood proudly making no attempt to stop them.”

“This should not be happening in modern America. And the fact Donald Trump is not just allowing it to happen, but actively encouraging it to happen, is an indefensible disgrace,” he continued. “The President keeps insisting he’s not a racist, and I’ve repeatedly said that in the 13 years I’ve known him, I’ve personally never witnessed him being a racist. But since running for the White House, his inflammatory language has flirted ever closer to crossing the line into overt racism, and now he’s crossed that line. Big time.”

Mr. Morgan ended his piece by calling on Mr. Trump to “stop this dangerous nonsense immediately” before someone gets hurt.

The column comes a day after Mr. Trump stood at the podium and watched as rally attendees broke into a chant of “send her back” after he accused Ms. Omar of spreading “vicious” anti-Semitism. After being roundly criticized for failing to condemn the chant at the moment, Mr. Trump later admitted that he disagreed with the sentiment.

“I was not happy with it. I disagree with it,” the president told reporters on Thursday.

Mr. Trump sparked an uproar earlier this week after he told the four Democratic congresswomen of color known as “The Squad,” which includes Reps. Omar, Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan and Ayanna Pressley of Massachusetts, that they should “go back” to their countries of origin. The president has refused to retract the comment despite widespread allegations of it being racist.