WASHINGTON (AFP) - Donald Trump cannot run for the presidency again and Republicans were wrong to support his campaign to reverse the 2020 election results, his former ambassador to the UN and a longtime loyalist Nikki Haley said in an interview published on Friday (Feb 12).

Haley, a fervent backer of the ex-president now on trial in the Senate for encouraging insurrection, told Politico Magazine that she is "deeply disturbed" by what has happened to Trump since his election defeat to Joe Biden.

"He's not going to run for federal office again," said Haley, who served as Trump's envoy to the United Nations from 2017-2018.

The former South Carolina governor dismissed speculation that, to avenge his defeat and second impeachment, Trump will return to seek the presidency in 2024.

"I don't think he's going to be in the picture," she said. "I don't think he can. He's fallen so far."

Haley also criticised the Republican Party for supporting Trump's campaign to reverse the election, which led to the shocking Jan 6 attack on Congress by his supporters.

"We need to acknowledge he let us down," she told Politico.

"He went down a path he shouldn't have, and we shouldn't have followed him, and we shouldn't have listened to him," she said.

"And we can't let that ever happen again."

Haley confirmed to Politico that she is considering her own run for the presidency in 2024, and said she had not spoken to Trump since Jan 6.

She suggested that Trump's legions of followers, who believed his claims of election fraud and who blame the Capitol attack on the left, need reeducation.

"They've been lied to by everybody," she said.

The comments came out as Trump's Senate trial for inciting insurrection entered its fourth day, with his defence lawyers preparing to rebut scathing evidence presented by Democratic prosecutors that the Jan 6 attack was the culmination of a deliberate campaign by the former president to foment violence.

With Trump still a heavyweight influence in their party, most Republican senators - including several themselves already setting the groundwork for a 2024 run - are expected to remain loyal, assuring he will not be convicted.

But eyes are on just how many will accept the evidence and vote to convict him, siding with Democrats to condemn his behaviour.