Former US president Donald Trump, having been criminally charged in New York, pledged Tuesday to “never drop out” of the 2024 race for the White House, and insisted Joe Biden is not fit to run again.

The Republican real estate magnate, facing 34 felony counts in New York over alleged hush money paid to an adult film actress, told Fox News anchor Tucker Carlson that nothing would prevent him from running — even a conviction.

“I’d never drop out,” he said. “It’s not my thing. I wouldn’t do it.”

Trump, 76, in his first major interview since being arrested and fingerprinted last week, cast doubt on whether Democrat Biden, 80, would be in the 2024 race.

“I don’t see how it’s possible,” he said.

“It’s not an age thing… I don’t think he can.

“I just don’t see Biden doing it from a physical or a mental standpoint. I don’t see it.”

Trump and other senior Republicans have repeatedly doubted Biden’s mental acuity and apparent frailty.

Right-wing outlets like Fox News frequently highlight his verbal flubs and moments where he appears to have lost his train of thought.

Throughout his own presidency, Fox offered an uncritical forum for Trump to air his grievances, with the then-commander-in-chief sometimes calling in unannounced to shows and talking at length to presenters.

The relationship cooled after Trump’s defeat to Biden at the ballot box in 2020 but has steadily grown again as the Republican nominating contest heats up.

The Interview, part two of which is expected to be broadcast on Wednesday, comes weeks after texts emerged showing Carlson speaking disparagingly about Trump after his election loss.

The messages were uncovered as part of a $1.6 billion lawsuit brought by Dominion Voting Systems against the Rupert Murdoch-run Fox News over its coverage of Trump and his allies’ unfounded claims of widespread fraud in the 2020 election.

“We are very, very close to being able to ignore Trump most nights. I truly can’t wait,” says one Carlson text message sent two days before a Trump-supporting mob — inspired by the then president’s false claims of a “stolen election” — invaded the US Capitol in Washington.

“I hate him passionately,” says another.

No mention was broadcast of the texts or of other evidence produced in discovery. (AFP)

•Former US president Donald Trump

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