The four women on Monday night said they would not be silenced, and said Trump's tweets and rhetoric are a distraction from the issues they're working on including, immigration, healthcare and education.
At the rally, Trump began by verbally attacking Omar as the crowd chanted "send her back!"
"This type of racist, misogynistic and extremist political atmosphere has for decades only been seen on the peripheries of far-right white supremacist politics", the letter said.
The incident triggered a wave of criticism, and Trump later attempted to downplay it, saying he actually "disagreed" with the chants.
Mr Trump said the "ridiculous" attempts to impeach him were now "over".
"We can not be defined by this", said Walker, telling reporters that he raised the topic at the Pence breakfast.
Trump is showing no signs of backing down from his strategy of tying the Democratic Party to the four liberal lawmakers, even after a Democratic-led House voted to condemn his comments as racist.
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At the event on Crenshaw Boulevard, Biden went behind the counter to serve breakfast to community leaders before telling them about the need for criminal-justice reform and economic revitalization in predominantly black neighborhoods.
"Every single member of this institution, Democratic and Republican, should join us in condemning the President's racist tweets". At the center of the dispute was Trump's Sunday tweet telling the four congresswomen to "go back" to their countries to fix them before attacking the United States, even though all four are US citizens and only Omar was not born in the country.
Mr Trump's overall approval remained unchanged over the past week. On Tuesday, after a bitter partisan brawl, House lawmakers approved a resolution to formally denounce Mr. Trump's recent tirade against four progressive congresswomen of color, with four Republicans joining Democrats to rebuke the president.
Yesterday it emerged that Omar has been United States citizen longer than Melania Trump, but that didn't stop those at a 2020 rally in Greenville, North Carolina, chanting the hurtful remarks.
After Trump suggested they leave the country, the crowd cheered in response: "Send them back!"
On Wednesday's Late Night, Seth Meyers took to task Republican leaders who are insisting that President Trump's "latest racist comments are not at all racist, despite the fact the they are definitely super racist".
It comes after a separate poll found the USA president's approval rating rose among Republicans after the United States president told the congresswomen to "go back" to where they came from.