A US federal judge on Thursday rejected former president Donald Trump's bid to dismiss charges that he mishandled classified documents after leaving the White House.

The Republican presidential candidate had claimed, in seeking to have the charges thrown out, that he had a right to keep the documents under the Presidential Records Act.

District Judge Aileen Cannon, a Trump appointee, denied Trump's motion, but left open the possibility the issue could be raised again at trial.

"The Presidential Records Act does not provide a pre-trial basis to dismiss," Cannon said in a brief order.

Trump, 77, pleaded not guilty in June to federal charges of unlawfully retaining national defence information, conspiracy to obstruct justice and making false statements.

He kept the classified files – which included records from the Pentagon, CIA and National Security Agency – unsecured at his Mar-a-Lago home in Florida and thwarted official efforts to retrieve them, according to the indictment.

Special counsel Jack Smith, who brought the charges against Trump, had threatened to take the case to an appeals court after Cannon indicated that the Presidential Records Act has merit in the case. The judge had asked for each side to propose jury instructions that would be based on a reading of the act.

While handing Smith a partial victory in refusing to toss the case based on the Presidential Records Act, Cannon defended her request for draft jury instructions saying it "should not be misconstrued."

"Nor should it be interpreted as anything other than what it was: a genuine attempt, in the context of the upcoming trial, to better understand the parties' competing positions," she said.

Prosecutors have proposed a July 8 start for the trial, but Cannon has not yet set a date and is yet to rule on a number of other motions brought by Trump's attorneys.

Trump also faces federal charges and an indictment in Georgia for allegedly conspiring to overturn the results of the 2020 election won by Democrat Joe Biden.

The judge presiding over the Georgia case rejected a motion by Trump on Thursday seeking to have it dismissed on the grounds it violated his free speech rights.

Trump's attorneys have sought to delay his various cases until after the November presidential election, when Trump could potentially have the federal charges against him dropped if he wins.

Trump is scheduled to go on trial in New York on April 15 on state charges of falsifying business records by paying pre-election hush money to a porn star. (AFP)