As thousands chanted “Send her back!” at a campaign rally Wednesday night in Greenville, N.C., the president paused to let it amplify.

He listened for 13 seconds, as the stray shouts stretched into a uniform roar. Some raised campaign signs or fists to the rhythm of the crowd as they yelled. Some only murmured along. A few were children, following the lead of the adults sitting in front-row seats behind President Trump.

“Send her back! Send her back!” they yelled in unison, advocating for deporting Rep. Ilhan Omar (D-Minn.), an American citizen and refugee, to Somalia, where she was born.

The chanting echoed Trump’s own racist comments on Sunday, when he suggested that four minority congresswomen, including Omar and Reps. Alexandria Ocasio-Cortez (D-N.Y.), Rashida Tlaib (D-Mich.) and Ayanna Pressley (D-Mass.) “go back and help fix the totally broken and crime infested places from which they came” rather than remain in the United States.

But while Trump’s response to the condemnation was familiar — doubling down, with the support of an enthusiastic crowd — Wednesday’s chanting alarmed many observers who suggested that the president’s invective could endanger the safety of the minority congresswomen and feed the country’s ugliest impulses.

“This is the sound of illiberalism, intolerance,” Jonathan Greenblatt, CEO of the Anti-Defamation League, said on Twitter. “Listen closely: it’s a danger not just to immigrants and minorities but to all Americans.”

Thousands spoke out to support Omar under the hashtag #IStandWithIlhan, with some of Omar’s constituents sending prayers “for Ilhan Omar and her family’s safety, peace of mind, and joy,” as one woman from Minneapolis said.

Democratic presidential candidates joined, with Sen. Kamala D. Harris (D-Calif.) calling the chant “vile,” “racist” and “cowardly” and Sen. Bernie Sanders (I-Vt.) saying Trump is “stoking the most despicable and disturbing currents in our society.” Some identified the “Send her back!” chant as the new “Lock her up!” — carrying the same feverish intensity as the unofficial 2016 campaign slogan targeting Hillary Clinton. Sen. Kirsten Gillibrand (D-N.Y.), a presidential candidate, said that in both cases the “throughline is contempt for women and anyone who threatens this president’s fragile ego.”

But for many, the most concerning aspect was that the chant reflected the racist “go back to where you came from” trope used by Trump, showing how the president’s xenophobic rhetoric tends to reverberate with approval among certain groups in his base.

“Now they don’t even have the false pretext of alleged corrupt behavior,” said Sen. Brian Schatz (D-Hawaii), referring to the “Lock her up!” chant. “They are just telling an American with whom they disagree to go back to Africa.”

The chant broke out after Trump spent several minutes bashing Omar and suggesting she is un-American, building the momentum that would morph into shouting. He repeated the false claim that she has supported al-Qaeda and said she “minimized the September 11 attacks on our homeland,” referring to a previous comment of Omar’s.

“She looks down with contempt on hard-working Americans, saying that ‘ignorance is pervasive in many parts of this country,’” Trump said just before the chant broke out.

“This is not cute, witty, or benign. This is malignant, dangerous, violent, white supremacist hatred targeting a sitting member of Congress, @IlhanMN, a Black woman, a Muslim,” Bishop Talbert Swan, a pastor and leader of the NAACP in Springfield, Mass., wrote on Twitter with the #IStandWithIlhan hashtag. “This vitriolic racist, antipathy puts her life in danger.”

Many of the president’s most reliable supporters insisted that neither his comments earlier this week nor the chant were racist, suggesting his true message is that Omar should leave because she is critical of America. But even some of Omar’s harshest conservative critics said Wednesday’s rally crossed the line.

Ryan Saavedra, a reporter at the conservative outlet the Daily Wire, told his followers that it’s “okay to be angry at Omar” but that “threats of violence and acts of violence are never okay.” He also wrote, “Like it or not, Omar is a U.S. Citizen and you can’t deport a U.S. citizen.”

Conservative radio host Hugh Hewitt called “Send her back!” a “nativist, terrible chant.” Guy Benson, political editor at the conservative website Townhall.com and a Fox News contributor, urged Omar’s critics to chant “Vote her out!” if they don’t like her policies, not “Send her back!” — a slogan he called “appalling.”

“I’m very tough on Omar [because] she deserves it, on the merits. I am sickened by the hate-laced ‘send her back’ chants,” Benson wrote. “Shame on every person who participated. POTUS has a responsibility to put an end to it. He alone has the ability to do so.”

Rep. Mark Walker, a Republican from North Carolina, voiced more measured displeasure with the chant, while still accusing Omar of having “disdain” for America and Israel. Trump had invoked past criticism of Omar for comments she made about Israel that were called anti-Semitic by members of both parties; she has apologized for those comments and insisted her criticism of Israel is rooted in its treatment of the Palestinians, not anti-Semitism.

“Though it was brief, I struggled with the ‘send her back’ chant tonight referencing Rep. Omar,” Walker wrote on Twitter. “Her history, words & actions reveal her great disdain for both America & Israel. That should be our focus and not phrasing that’s painful to our friends in the minority communities.”

Former Illinois Republican congressman Joe Walsh was more blunt: “'SEND HER BACK, SEND HER BACK,' is ugly. It’s ignorant. It’s dangerous. And it’s un-American. It’s flat out bigotry. And every Republican should condemn this bigotry immediately. Stop this now."

Few elected Republicans, however, weighed in on Wednesday night.

Omar responded with a quote from Maya Angelou. “You may shoot me with your words/ You may cut me with your eyes/ You may kill me with your hatefulness/ But still, like air, I’ll rise.”

She then said: “I am where I belong, at the people’s house and you’re just gonna have to deal!”