Donald Trump will face serious charges of willfully keeping highly classified documents at his Florida home in a trial set for May 20 next year by federal judge Aileen Cannon.

The indictment unveiled last month says Trump kept the files — which included top secret nuclear and defense documents from the Pentagon, CIA and National Security Agency — unsecured at his Mar-a-Lago estate in Palm Beach, Florida.

The former president took the documents with him as he left the White House in 2021, against US law which requires all presidential records to be handed over to the National Archives.

Prosecutors say Trump was given multiple opportunities to return the documents and they raided Mar-a-Lago in August last year after obtaining evidence that he knowingly retained more than 100 classified files.

Boxes and folders with the secret documents were hidden in Trump’s private office, a ballroom, a bathroom, his bedroom and a storage room, according to the indictment.

On at least two occasions, prosecutors alleged, Trump showed classified documents on US military operations and plans to people not cleared to see them, at his Bedminster, New Jersey, golf club.

“The classified documents Trump stored in the boxes included information regarding defense and weapons capabilities of both the United States and foreign countries,” the indictment said.

“The unauthorized disclosure of these classified documents could put at risk the national security of the United States, foreign relations, the safety of the United States military, and human sources,” according to the indictment.

The indictment lists 37 separate counts against Trump.

They include 31 counts of “willful retention of national defense information,” each count relating to a specific document he kept.

The documents listed included information on US nuclear programs and potential vulnerabilities of the United States and its allies to military attack, along with plans for retaliation, according to the indictment.

A conviction on each of the 31 “willful retention” charges carries up to 10 years in prison.

The six other charges include conspiracy to obstruct justice, punishable by up to 20 years in prison; withholding a document or record, which also carries a potential 20-year sentence; and making false statements.

Trump’s personal aide, Walt Nauta, will stand trial together with him.

Nauta was named as a co-conspirator and charged with six counts for helping Trump hide documents in Mar-a-Lago.

Trump and Nauta both entered pleas of not guilty. Trump claims that as a former president he had a right to retain documents.

He also has said that using his authority of president he had declassified the documents in question, though he has not offered evidence to support that claim.