US president Donald Trump has turned a campaign rally into an extended dissection of the liberal views of four Democratic congresswomen, deriding them for what he painted as extreme positions and suggesting they leave America.

“Tonight I have a suggestion for the hate-filled extremists who are constantly trying to tear our country down,” Mr Trump told the crowd in North Carolina.

“They never have anything good to say. That’s why I say, ‘Hey if you don’t like it, let ’em leave, let ’em leave’.”

Mr Trump’s jabs were aimed at the self-described “squad” of four Democrats who have garnered attention since their arrival in January for their outspoken views and distaste for the president: Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota, Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan.

All were born in the US except for Omar, who arrived there as a child after fleeing Somalia with her family.

Taking the politicians on one at a time, Mr Trump ticked through a list of what he deemed offensive comments by each woman, misconstruing many facts along the way.

Ms Omar came under the harshest criticism as Mr Trump played to voters’ grievances, drawing a chant from the crowd of “Send her back! Send her back!”

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Donald Trump at the rally in Greenville (Gerry Broome/AP)

The president began his attack on Sunday when he tweeted that the four should “go back” to their home countries. He has accused them of “spewing some of the most vile, hateful and disgusting things ever said by a politician”.

Before he left Washington, Mr Trump said he has no regrets about his ongoing row with the four. The president told reporters he’s “winning the political argument” and “winning it by a lot”.

“If people want to leave our country, they can. If they don’t want to love our country, if they don’t want to fight for our country, they can (leave),” Mr Trump said. “I’ll never change on that.”

His speech was filled with criticisms of the news media, which he says sides with liberals, and of special prosecutor Robert Mueller’s Russia probe.

Mr Mueller had been scheduled to testify to Congress on Wednesday, but it was postponed.

“What happened to me with this witch hunt should never be allowed to happen to another president,” Mr Trump said.

He also talked about illegal immigration, a main theme of his first presidential bid that is taking centre stage in his re-election campaign.

The president brushed off the criticism he has got for saying that the congresswomen should go back home. “So controversial,” he said sarcastically.

The four politicians say they are fighting for their priorities to lower health care costs and pass a Bill addressing climate change, while his attacks are a distraction and tear at the core of America values.

The Democratic-led House of Representatives voted on Tuesday to condemn Mr Trump for what it labelled “racist comments”, despite opposition from all bar four Republicans and the president’s insistence that he does not have a “racist bone” in his body.

The condemnation carries no legal repercussions and Mr Trump’s latest harangues struck a chord with supporters in Greenville, who chanted “Four more years!” and “Build that wall!”

It was Mr Trump’s sixth visit to the state as president and his first 2020 campaign event in North Carolina, where he defeated Democratic nominee Hillary Clinton in 2016.