The legal battle threatens Trump's bid for a presidential comeback next year/ Photo: AP

Donald Trump is due in court Tuesday to face dozens of felony counts of mishandling US government secrets, in the most serious yet of a firestorm of criminal probes threatening to derail his bid to win back the White House.

The former president plans to travel by motorcade for the 25-minute journey from his golf course in Miami to the federal courthouse, where he is expected to deny 37 counts of unlawfully retaining classified documents and obstructing efforts to get them back.

The Republican leader is running for reelection, and devoted supporters had already begun hitting the streets on the eve of the hearing - with Miami police bracing for protests of up to 50,000 and prepared for the possibility of violence.

"There's never been anything like it. A witch hunt like this has never taken place," Trump told a local conservative Hispanic radio station after arriving in Miami from his summer home in New Jersey on Monday.

"When you look at what they've done, and when you look at the criminal acts and the horrible acts that they've committed, and then they come after me."

The billionaire politician, who turns 77 on Wednesday, is accused of willfully hoarding dozens of clearly-marked government secrets he took unlawfully to his beachfront mansion in Florida when he left office in 2021, refusing to return them and conspiring to obstruct investigators seeking to recover them.

He is also charged with sharing sensitive US secrets with people who had no security clearance, in a much more serious case than any he has previously faced, with charges that can carry decades-long prison sentences.

AFP