Former President Donald Trump and an aide have arrived at the federal courthouse in downtown Miami to be arrested and arraigned on federal charges.

The criminal charges in the Justice Department's classified documents case escalates the legal jeopardy surrounding the 2024 GOP front-runner.

Tuesday's hearing, at 3 p.m. ET in Miami, is expected to be procedural in nature. Trump will enter a plea, there will be a discussion of the conditions of his pretrial release, and it's possible that potential restrictions around Trump's conduct as the case moves forward are brought up.

Trump is facing 37 felony counts, alleging he illegally retained national defense information and that he concealed documents in violation of witness-tampering laws in the Justice Department's probe into the materials.

His close aide, Walt Nauta, was also charged in the indictment, unsealed Friday, which alleges the two men engaged in a conspiracy to obstruct the federal investigation. Nauta also will be appearing in court.

Trump left his Doral resort in his motorcade Tuesday along with Nauta, who was traveling in a separate vehicle. As he got in his vehicle, a bystander asked Trump how he was feeling. Trump said "great" and waved.

On his social media, Trump posted before heading to court that it was "ONE OF THE SADDEST DAYS IN THE HISTORY OF OUR COUNTRY. WE ARE A NATION IN DECLINE!!!"

Tuesday's hearing will kickstart what will likely be a winding, dramatic judicial process, with criminal and appeal proceedings that may play out for years. US District Judge Aileen Cannon -- a Trump nominee whose decision last year to order a third-party review of an FBI search of Mar-a-Lago was widely criticized and overturned by a conservative appeals court -- has been assigned the case.

Tuesday's proceedings will be overseen by a magistrate judge, expected to be Jonathan Goodman, who is the magistrate on duty in Miami this week.

What Tuesday's hearing is about

Tuesday's hearing will operate as both an "initial appearance" and as a so-called arraignment as well, with Trump having the opportunity to enter his plea in the case.

Trump and Nauta's lawyers will enter appearances in court on their behalf, and Florida rules require that the defendants have at least one lawyer barred in the state representing them.

Attorneys Todd Blanche and Chris Kise are expected to represent Trump in court this afternoon for his arraignment, a source familiar with the matter tells CNN. However, the role Kise will play going forward is unclear, and he was sidelined during last year's litigation over the Mar-a-Lago search amid Trump team in-fighting.

Another Florida-licensed attorney, Lindsey Halligan -- who also worked on Trump's lawsuit last year over the search -- remains on Trump's team and may be present Tuesday.

Both defendants will be subjected to booking by the US Marshals Services as part of Tuesday's events, though under Justice Department rules, their mug shots will not be immediately publicly available.

At the hearing, the magistrate judge will discuss the bond package that will allow the defendants to remain out of detention while they await trial. There might be requirements that they notify the court's probation's office before traveling to certain location. Prosecutors also might ask that restrictions be placed on Trump and Nauta barring their communications with witnesses.

The Justice Department's counterintelligence chief Jay Bratt, who has been a key player in the documents probe so far, is listed on the case's document as representing the government. But it's likely that lawyers from the Southern District of Florida's US Attorney's office -- which is led by US Attorney Markenzy Lapointe, who was confirmed by the Senate in December -- are present Tuesday as well. It's unclear who from Smith's team will be at the proceedings, or if Smith himself will show up.

Seriousness of the charges

Before last week's federal indictment, Trump also faced criminal charges brought by New York City's local prosecutors for an alleged hush money scheme in the 2016 campaign in which Trump is accused of falsifying business records.

The new charges in the DOJ documents case are drastically more serious and present the possibility of several years in prison if Trump is ultimately convicted.

Thirty-one counts that Trump faces are for willful retention of national defense information, a charge that does not turn on whether the documents are classified. In addition to the obstruction conspiracy, he also faces four counts related to the concealment of the documents, as well as a false statements charge.

"In a case like this, obstruction and tampering help prove the main charge, that the defendant willfully engaged in the charged conduct," said David Aaron, a former federal prosecutor in espionage section of the DOJ's national security division and a current senior counsel at Perkins Coie. "Those facts could also affect how a judge, the jury, or the public views the case and could substantially affect sentencing."

What happens next

Once Tuesday's hearing is in the rearview mirror, the case will enter a legal grind of pretrial proceedings, including likely disputes over what evidence is put before a jury and whether the case should be thrown out altogether before going to trial. The Trump team will have plenty of opportunity to drag things out -- potentially until after the 2024 election.

One major x-factor in the prosecution of the case is its assignment to Cannon, who sits in Ft. Pierce, Florida, but who is part of the pool of judges who are randomly cases filed in West Palm Beach, where the new indictment was brought.

"There are few things more powerful than a district judge in a federal case," said Alan Rozenshtein, a former attorney in the DOJ National Security Division who is now a University of Minnesota law school professor. "She could -- if she wanted to -- cause huge problems for the prosecution. Would they be existential problems? Probably not."

Cannon's approach to last year's Trump lawsuit challenging the FBI's Mar-a-Lago search raised eyebrows among legal experts across the ideological spectrum for how she appeared to bend over backward to create special legal rules in favor of the former president. Her rationale for why such a review was necessary was torn apart by a panel of right-leaning appellate judges, including two Trump appointees, on the 11th US Circuit Court of Appeals last December.

"She got so banged up by the 11th Circuit that she might be ultra-cautious," Kel McClanahan, a national security lawyer and an adjunct professor at the George Washington University Law School, told CNN. "We just don't know."

This story has been updated with additional developments.