WASHINGTON — President Trump said on Sunday that a group of four minority congresswomen feuding with Speaker Nancy Pelosi should “go back” to the countries they came from rather than “loudly and viciously telling the people of the United States” how to run the government.

Wrapped inside that insult, which was widely established as a racist trope, was a factually inaccurate claim: Only one of the lawmakers was born outside the country.

Even though Mr. Trump has repeatedly refused to back down from stoking racial divisions, his willingness to deploy a lowest-rung slur — one commonly and crudely used to single out the perceived foreignness of nonwhite, non-Christian people — was largely regarded as beyond the pale.

“So interesting to see ‘Progressive’ Democrat Congresswomen, who originally came from countries whose governments are a complete and total catastrophe, the worst, most corrupt and inept anywhere in the world,” Mr. Trump wrote on Twitter, “now loudly and viciously telling the people of the United States, the greatest and most powerful Nation on earth, how our government is to be run.”

Mr. Trump added: “Why don’t they go back and help fix the totally broken and crime infested places from which they came. Then come back and show us how it is done.”

Delivered on the day he had promised widespread immigration raids, Mr. Trump’s comments signaled a new low in how far he will go to affect public discourse surrounding the issue. And if his string of tweets was meant to further widen Democratic divisions in an intraparty fight, the strategy appeared quickly to backfire: House Democrats, including Ms. Pelosi, rallied around the women, declaring in blunt terms that Mr. Trump’s words echoed other xenophobic comments he has made about nonwhite immigrants.

[When it comes to race, Mr. Trump plays with fire like no other president in a century.]

As the president’s remarks reverberated around Twitter, a chorus of Americans took to social media to say that they had heard some version of Mr. Trump’s words throughout their lives, beginning with childhood taunts on the playground. Senator Cory Booker, Democrat of New Jersey and a presidential candidate, joined scores of people who said it was jarring to hear the phrase from the president.

“We’ve heard this our whole lives,” Mr. Booker said. “Now we hear it from the Oval Office.”

Ms. Pelosi may have offered the bluntest take on Mr. Trump’s comments when she said his campaign slogan, “Make America Great Again,” “has always been about making America white again.”

Broadly, Mr. Trump’s attack on lawmakers appeared to be meant for members of the so-called squad, a group of liberal Democratic freshmen engaged in an existential and generational war of words with Ms. Pelosi: Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota, Rashida Tlaib of Michigan and Ayanna S. Pressley of Massachusetts.

But only one of the women, Ms. Omar, who is from Somalia, was born outside the United States. Ms. Ocasio-Cortez was born in the Bronx to parents of Puerto Rican descent. Ms. Pressley, who is black, was born in Cincinnati and raised in Chicago. And Ms. Tlaib was born in Detroit to Palestinian immigrants.

“These places need your help badly, you can’t leave fast enough,” Mr. Trump said. “I’m sure that Nancy Pelosi would be very happy to quickly work out free travel arrangements!”

Mr. Trump’s comments were a crude addition to his continued rhetoric that the United States is too full to take in people from other countries. “Sorry, can’t let them into our Country,” Mr. Trump also tweeted on Sunday, referring to the groups of men held in filthy conditions in detention centers at the border. He suggested that those groups were “loaded up with a big percentage of criminals.”

His tweets came on the same weekend that Immigration and Customs Enforcement agents began rounding up some 2,000 undocumented immigrants, many of whom had recently crossed the border in groups or families.

Mr. Trump’s attack on the congresswomen also followed days of Fox News coverage that centered on Ms. Omar. During her tenure in Congress, Ms. Omar has rattled fellow Democrats and provided ammunition to Republicans for her repeated criticisms of Israel, including a comment that pro-Israel activists were pushing “for allegiance to a foreign country.”

Prompted by an emergency border aid package that liberals felt did not place sufficient restrictions on the Trump administration, the back and forth between the freshmen women, Democratic moderates in the House and Ms. Pelosi has also been bruising.

The speaker spent much of the last week trying to return harmony to her restive caucus, and tensions were still raw heading into the weekend. When Ms. Ocasio-Cortez’s chief of staff, Saikat Chakrabarti, singled out Representative Sharice Davids, a moderate Democrat and Native American from Kansas, for voting in favor of the aid package, House Democrats used their official Twitter account to slap back. “Who is this guy and why is he explicitly singling out a Native American woman of color?” they wrote.

On Sunday, Mr. Trump may have provided the impetus for a reconciliation — however brief — that Democratic leaders and rank-and-file House members quickly embraced.

Ms. Pelosi condemned Mr. Trump’s remarks as “xenophobic” in a pair of tweets of her own, turning them around to criticize Mr. Trump’s immigration policies and project Democratic unity. “Our diversity is our strength and our unity is our power,” she wrote of Democrats.

When @realDonaldTrump tells four American Congresswomen to go back to their countries, he reaffirms his plan to “Make America Great Again” has always been about making America white again.

Our diversity is our strength and our unity is our power. https://t.co/ODqqHneyES

— Nancy Pelosi (@SpeakerPelosi) July 14, 2019

“Rather than attack Members of Congress, he should work with us for humane immigration policy that reflects American values,” she wrote in another tweet. “Stop the raids.”

A spokesman for Senator Mitch McConnell, the majority leader, declined to comment on Mr. Trump’s remarks. Representatives for Republican House leaders did not respond to emails seeking comment. The White House also did not respond to a request for comment. But Democrats began sharing their own stories, pointing out that Mr. Trump’s remarks did not reflect a country whose lawmakers — and citizens — are becoming increasingly more diverse.

Growing up I used to hear “go back to Mexico” from many kids, though I was born in the USA. I thought then that it was just kids. https://t.co/BguGAwQP0S

— Ruben Gallego (@RubenGallego) July 14, 2019

Representative Joaquin Castro, Democrat of Texas and the chairman of the Congressional Hispanic Caucus, called Mr. Trump a “bigot.” Representative Justin Amash of Michigan, who left the Republican Party this month over differences with Mr. Trump and is the child of Syrian and Palestinian immigrants, declared the comments “racist and disgusting.”

To tell these American citizens (most of whom were born here) to “go back” to the “crime infested places from which they came” is racist and disgusting. https://t.co/sIAqg8bTIb

— Justin Amash (@justinamash) July 14, 2019

All four lawmakers in “the squad” eventually weighed in and responded to the president. “You are stoking white nationalism,” Ms. Omar said, because “you are angry that people like us are serving in Congress and fighting against your hate-filled agenda.”

Ms. Pressley, sharing a screenshot of the president’s tweet, declared, “THIS is what racism looks like.” Ms. Tlaib said his comments “just make me work harder,” and that she is “fighting corruption in OUR country.” And Ms. Ocasio-Cortez sent out a series of tweets addressing the president directly. “Mr. President,” she said in one, “the country I ‘come from’ & the country we all swear to, is the United States.”

Mr. President, the country I “come from,” & the country we all swear to, is the United States.

But given how you’ve destroyed our border with inhumane camps, all at a benefit to you & the corps who profit off them, you are absolutely right about the corruption laid at your feet. https://t.co/HLKQCotR8T

— Alexandria Ocasio-Cortez (@AOC) July 14, 2019

But by Sunday evening, Mr. Trump again criticized Democrats for defending members of the group. “If the Democrat Party wants to continue to condone such disgraceful behavior,” Mr. Trump said on Twitter, “then we look even more forward to seeing you at the ballot box in 2020!”

Ms. Omar and Ms. Tlaib are far from the only congressional lawmakers who immigrated to the United States or were born to immigrant parents. In the House, there are currently at least 52 voting members who are immigrants or children of immigrants and 16 in the Senate — most of them Democrats — according to a Pew Research Center analysis from this year. Aside from Ms. Omar, four other congresswomen were born outside the United States, but they have largely not involved themselves in entanglements with Ms. Pelosi.

Ms. Omar has been vocal about her life as a refugee who fled Somalia and eventually settled in America, only to be disappointed with the country she found. More than any of the others in her freshman group, Ms. Omar — one of the first two Muslim women in Congress along with Ms. Tlaib — has forcefully used her personal story to make the argument that loving America does not require an acceptance of its shortcomings.

“I grew up in an extremely unjust society, and the only thing that made my family excited about coming to the United States was that the United States was supposed to be the country that guaranteed justice to all,” Ms. Omar recently said. “So, I feel it necessary for me to speak about that promise that’s not kept.”

Comments like these have inflamed Fox News personalities like Tucker Carlson, who used his television program to lash out at Ms. Omar.

“Our country rescued Ilhan Omar,” Mr. Carlson said in a broadcast last week. “We didn’t do it to get rich; in fact, it cost us money. We did it because we are kind people. How did Omar respond to the remarkable gift we gave her? She scolded us, and called us names, she showered us with contempt.”

Mr. Trump has repeatedly said that he does not hold racist views, despite his public statements. After a 2017 white nationalist rally in Charlottesville, Va., Mr. Trump was widely condemned for saying that people on “both sides” were to blame after one of the nationalists mowed down a group of protesters and killed a woman. And he was one of the most vocal proponents of the conspiracy theory that President Barack Obama was not born in the United States.

At other times, he has used vulgar language to describe immigrants and people of color. He has defended himself after calling people crossing into the country illegally “animals” — he said was referring only to MS-13 gang members. He has assailed players with the National Football League, many of whom are black, for taking a knee during the national anthem. And he has used a vulgar term to disparage immigrants from largely black nations.

But, to his critics, Mr. Trump’s comments on Sunday were a low point.

“It is sad to see the occupant of the Oval Office transition from empowering and encouraging racist taunts to actually using them himself,” said Nihad Awad, the national executive director of the Council on American-Islamic Relations. “If Trump shouted the same thing at a Muslim woman wearing hijab in a Walmart, he might be arrested.”

A version of this article appears in print on July 15, 2019, Section A, Page 1 of the New York edition with the headline: Fanning Flames, Trump Unleashes a Taunt: ‘Go Back’.