Former US President Donald Trump will be formally charged at a court hearing on Thursday on charges of plotting to overturn his 2020 election defeat.
On the eve of the arraignment he slammed the case as proof of the “corruption, scandal, & failure” of the US under Joe Biden’s presidency.
Mr Trump already faces two other criminal cases as he campaigns for the White House next year.
Security is being ramped up in Washington DC for Thursday’s hearing.
Metal barriers have been put up outside the federal courthouse where the charges against Mr Trump will be formally read.
Similar structures have been erected around the US Capitol buildings, where Trump supporters rioted in January 2021, angry at the election result.
The Secret Service, which provides protection to presidents and ex-presidents, released a statement warning the public of “short-term traffic implications” in central Washington DC.
On Wednesday, an apparent hoax 911 call about an active shooting at the Capitol triggered a lockdown in three Senate office buildings and a major police emergency response.
Speaking to reporters during the alert, US Capitol Police Chief Tom Manger said the police force that battled rioters two-and-a-half years ago was well-trained and prepared for active-shooter drills.
Protection for judges involved in the case has also reportedly been increased.
That includes District Judge Tanya Chutkan, who told an attorney in an unrelated case that she had not slept since being assigned to Mr Trump’s case, to which the lawyer replied: “Please be safe”.
“I’ll try,” Ms Chutkan said before an open court, later joking that she wanted to keep her calendar open “in case I can get out of town, which is increasingly looking like a good idea”.
Mr Trump, 77, is due to appear at a federal courthouse in Washington DC on Thursday at 16:00 EDT (20:00 GMT). He is expected to plead not guilty. Although he has the option of appearing remotely via video feed, it is understood he will attend in person.
Mr Trump has visited the city only once since leaving the White House. A queue was already forming on Wednesday evening outside the building.
In an all-capital-letters post on his Truth Social platform on Wednesday, the former president, who was at his Bedminster, New Jersey, golf club, thanked his followers and said: “I never had so much support on anything before.”
In other posts he attacked rival Republican presidential hopefuls, including his former Vice-President Mike Pence and Florida Governor Ron DeSantis.
He repeated his argument that Mr Pence had had the legal authority to stop Congress from certifying Mr Biden’s election victory on 6 January 2021, proceedings that were disrupted as Trump supporters rioted at the US Capitol.
According to the indictment, Mr Trump faces four counts, including conspiracy to defraud the US, tampering with a witness and conspiracy against the rights of citizens.
The deprivation of rights statute was enacted in the aftermath of the US Civil War to provide legal protections for freed slaves as they integrated into society.
The charge was key to a 1967 trial of Ku Klux Klan members that inspired the 1988 film Mississippi Burning. Legal analysts say it has been included in the case against Mr Trump because his alleged efforts to subvert the vote targeted urban areas with large populations of African-American voters.
