WAUKEE, Ia. — Former Vice President Joe Biden said President Donald Trump should "go home" after he penned a series of "flat racist" tweets against four minority Democratic congresswomen.

"As recently as the way he spoke about four members of Congress, women members of Congress. No matter what you think of their politics. He talked about going back to the awful countries they were from — Brooklyn, Michigan," Biden said to laughter. "But I mean, I mean, it's a flat racist attack. He said they should go home. He should go home."

Biden made the comments Monday in Waukee, Iowa, at the home of former Iowa Gov. Tom Vilsack, who hosted a house party for the former vice president.

Trump tweeted Sunday about Democratic Reps. Alexandria Ocasio-Cortez of New York, Ayanna Pressley of Massachusetts, Rashida Tlaib of Michigan, and Ilhan Omar of Minnesota.

"Why don’t they go back and help fix the totally broken and crime infested places from which they came," he wrote. "Then come back and show us how it is done."

The tweets were widely condemned as racist.

All four of the congresswomen were born in the United States with the exception of Omar, who came to the United States as a refugee from Somalia when she was young.

Trump has denied the comments were racist, telling reporters that "if you hate our country, if you're not happy here, you can leave.”

More:Donald Trump says the House Democrats he insulted should apologize day after his 'go back' tweets

Biden was campaigning in Iowa as part of a three-day swing across the state. He spoke earlier in the day at a forum hosted by the Des Moines Register and AARP about senior issues. There, he highlighted his new health care plan, an alternative to "Medicare for All", which would build on Obamacare.