A fired-up Donald Trump took aim once more at Democratic lawmakers who "hate" America as he hit the campaign trail Wednesday, hours after an opposition bid to impeach the US president over "racist" attacks was shot down in Congress.

Egging on a sea of supporters in Greenville, North Carolina, Trump reeled off the names of the ethnic minority congresswomen whom he has urged to "go back" to their countries of origin in a series of incendiary tweets.

"These left-wing ideologues see our nation as a force of evil," charged Trump - whose tweets were condemned as "racist" a day earlier by the House of Representatives, although a subsequent attempt to launch impeachment proceedings failed in the chamber.

"Send her back!" the crowd roared when Trump cited Ilhan Omar - one of just two Muslim women in Congress, whose criticism of Israel has been deemed anti-Semitic by many lawmakers.

"The way they speak so badly of our country," Trump told his supporters, decked out in the colors of the US flag and "Make America Great Again" caps. 

"They want to demolish our constitution. Eliminate the values that built this magnificent country."

Pouring scorn on all four congresswomen - known as "The Squad" - Trump aimed perhaps his harshest taunts at Alexandria Ocasio-Cortez, the outspoken New York lawmaker who has likened migrant detention centers at the Mexican border to concentration camps.

"I don't have time to go with three different names. We will call her Cortez," he mocked, to the crowd's delight.

Trump's attacks have widely been seen as a bid to rally his right-wing base as the 2020 White House race heats up - at the risk of inflaming racial tensions and deepening partisan divisions in America.

He himself has given credence to the notion, telling reporters he was "enjoying" his battle with the congresswomen "because I have to get the message out to the American people."