U.S. President Donald Trump tried to distance himself on Thursday from supporters' chants of "send her back" at a rally where he blasted Somalia-born U.S. Representative Ilhan Omar, as Republicans worry the incendiary mantra could set the tone for the 2020 campaign.

Omar, a Democrat, shot back that Trump was "spewing fascist ideology," and Republicans expressed alarm that the inflammatory chant, building off of provocative tweets and statements by Trump, might become a theme of his 2020 re-election campaign. 

"We cannot be defined by this," said conservative Representative Mark Walker, who added that Republican leaders in the House of Representatives discussed the potential political risks at a breakfast with Vice President Mike Pence.

"That does not need to be our campaign call," Walker said. 

He and other Republicans denounced the language used by Trump's supporters, which followed a weekend Twitter attack by Trump on Omar and three other Democratic lawmakers, all minority women, saying they should "go back" to where they came from. 

All four are U.S. citizens and, with the exception of Omar, were born in the United States. Known on Capitol Hill as "the squad," the four lawmakers are sharp critics of both Trump and the Democratic House leadership. Besides Omar, the other three are Alexandria Ocasio-Cortez, Rashida Tlaib and Ayanna Pressley. 

Their physical safety and security was emerging as an issue. House Homeland Security Committee Chairman Bennie Thompson asked the Capitol Police in a letter on Thursday for an emergency meeting to discuss the president's attacks on the four women. 

"Last night at a campaign rally, the president once again used inflammatory rhetoric about the four congresswomen," Thompson wrote, adding that the police department "must act swiftly to address heightened threats to these and other members of Congress." It followed a similar request Thompson made on Monday. 

Trump at midday tried to distance himself from the chant. At the White House, he told reporters: "I felt a little bit badly about it. ... I would say that I was not happy with it. I disagreed with it. But, again, I didn't say that. They did. And I disagreed with."

(Cover: U.S. President Donald Trump works the crowd during a campaign rally on July 17, 2019, at East Carolina University in Greenville, North Carolina. /VCG Photo)