Donald Trump is due to appear in court in Florida to face charges of mishandling sensitive documents after he left the White House.
The former president will enter a courthouse in Miami for an initial hearing on Tuesday, the second time he has appeared in court this year.
Miami’s police chief said the force was ready for crowds of between 5,000 and 50,000 people to gather.
Mr Trump spent the night at his hotel resort in the city.
The 76-year-old is expected to travel by motorcade from the Trump National Doral resort to the Wilkie D Ferguson Jr courthouse where his arraignment is scheduled for around 15:00 local time (19:00 GMT).
Following the 25-minute journey, Mr Trump will appear in front of a judge and is expected to deny 37 counts of illegally retaining classified documents and obstructing the government’s efforts to get them back.
The hearing will last for about an hour and will address various procedural issues, although it is unlikely a trial date will be set. A judge earlier rejected a request by news organisations to allow photo and video access inside.
Mr Trump, who has repeatedly denied wrongdoing, is then expected to return to his golf resort in Bedminster, New Jersey, where he will make remarks to the media.
The charges, which were made public on Friday, came after FBI agents found more than 100 documents with classified markings at Mr Trump’s private Florida estate Mar-a-Lago in August.
They allegedly contained information about the defence and weapons capabilities of both the US and foreign countries, as well as plans for possible retaliation in response to a foreign attack.
Prosecutors accuse him of hoarding the secret files, storing some in a ballroom and a bathroom, and of engaging in a conspiracy with an aide to obstruct the FBI’s inquiry.
Police officers and sniffer dogs have been patrolling the area surrounding the court in downtown Miami as officials warn of the potential for unrest.
“Make no mistake about it – we’re taking this event extremely serious,” Miami Police Chief Manuel Morales said. “We know that there is a potential of things taking a turn for the worse.”
Supporters of Mr Trump, who is the frontrunner for the Republican presidential nomination in 2024, have gathered outside his resort, with some carrying huge flags reading: “Donald Trump 2024, I’ll be back”. Cars and motorcycles covered in Trump paraphernalia also circled the area while others sounded their horns in support.
Mr Trump entered a restaurant at the resort on Monday evening, greeting supporters and posing for a picture. “With you all the way!” one person shouted from the bar, before Mr Trump thanked him and gave a thumbs up.
His legal troubles appear not to have diminished his support among Republican voters, and he continues to hold a significant lead over all other candidates for the nomination.
A poll by the BBC’s US partner CBS found 76% of likely Republican primary voters were more concerned about the indictment being politically motivated than about the documents posing a national security risk.
And a Reuters/Ipsos poll released on Monday returned a similar result, showing 81% of Republicans thought the charges were politically motivated, which is something Mr Trump has long claimed.
He has continued to strike a defiant tone as his moment in court nears, airing grievances with the case and repeatedly accusing the Biden administration of weaponising law enforcement agencies against him in an interview with a Spanish-language radio programme on Monday.
Long-standing protocol dictates that the Department of Justice, the federal agency that enforces US law, should operate independently from the White House. “I have never once – not one single time – suggested to the justice department what they should do,” President Biden said on Thursday.
Legal experts say the criminal charges could lead to substantial prison time if he is convicted. Mr Trump, however, has vowed to continue his campaign for president whatever the verdict.
He will appear in court alongside a close aide, Walt Nauta, who was charged by the same grand jury in Florida. Mr Nauta faces six criminal counts related to alleged handling of national security documents.
Mr Trump’s court appearance will be his second in less than three months. He was arraigned in April in New York on charges that he falsified business records for a hush-money payment to a porn star ahead of the 2016 election.