What could a possible prison sentence for Donald Trump look like?

Investigators for the Federal Bureau of Investigation who searched Harold Martin’s Maryland property in the fall of 2016 found classified documents — including material at the top-secret level — strewn about his home, car and storage shed.

Unlike former United States President Donald Trump, the former National Security Agency contractor did not contest the allegations: He ultimately pleaded guilty in 2019, admitting his actions were “wrong, illegal and highly questionable”.

But his expressions of contrition and guilty plea to a single count of willful retention of national defence information did not spare him the harsh punishment of nine years in prison.

The resolution of that case looms as an ominous guidepost for the legal jeopardy Trump could face as he confronts 37 felony counts — including 31 under the same century-old Espionage Act statute used to prosecute Martin and other defendants alleged to have illegally retained classified documents. Even many like Martin who have pleaded guilty and accepted responsibility have nonetheless been socked with years-long prison sentences.

“When they decide to pursue a willful mishandling case, it’s to send a message: that we take these cases very seriously,” said Michael Zweiback, a defence lawyer and former Department of Justice prosecutor. “They almost always are seeking jail time.”

How much prison time the former president could face in the event of a conviction is impossible to say. Such a decision is ultimately would largely be up to the trial judge — in this case, a Trump appointee who has already demonstrated a willingness to rule in his favour.

It’s also hard to know the extent to which other factors — including the logistical and political complications of jailing a former president — might play a role.

The Espionage Act offence is punishable by up to 10 years in prison, although it is rare for first-time federal offenders to get close to the maximum. But beyond Trump’s retention of classified documents, prosecutors have also identified multiple aggravating factors in the former president’s alleged conduct, accusing him of seeking to enlist others — including a lawyer and aides — to hide the records from investigators, as well as showing off some of the documents to visitors.

Other counts in the indictment, including conspiracy to obstruct justice, call for up to 20 years in prison.

Justice Department prosecutors in recent years have used the Espionage Act provision against a variety of defendants, including a West Virginia woman who retained an NSA document related to a foreign government’s military and political issues. Elizabeth Jo Shirley pleaded guilty in 2020 to a wilful retention count and was sentenced to eight years in prison.

This month, a retired Air Force intelligence officer named Robert Birchum was sentenced to three years in prison after pleading guilty to keeping classified files at his home, his overseas officer’s quarters and a storage pod in his driveway.

Many defendants have pleaded guilty, rather than face trial, though not all have gone to prison. Trump — who also faces charges related to hush-money payments in New York state court — has shown no signs that he could be headed towards a plea deal, vigorously insisting he is innocent and attacking Justice Department special counsel Jack Smith hours after appearing in Miami federal court on Tuesday.

Despite the details in the indictment, Trump does have some avenues to try to contest the charges.

For one thing, his case will be presented before Judge Aileen Cannon, who sided with Trump last year in the former president’s bid to appoint a special master to conduct an independent review of the seized classified documents. Citing the “stigma” associated with an FBI search of Trump’s home, she said a “future indictment” based on items that should have been returned to Trump “would result in reputational harm of a decidedly different order of magnitude”.

A three-judge panel of the US Court of Appeals for the 11th Circuit unanimously overturned her ruling, which was widely criticised by legal experts as extraordinary and unusually broad.

Over the next several months, Cannon will make decisions that will shape the trial, including how quickly it will happen and whether any evidence will be kept out.

Prosecutors also face the challenge in Florida — where Republicans have made steady inroads in recent years — of a jury pool likely to be more favourable to Trump than if the case were tried in overwhelmingly Democratic Washington, DC.

Still, “I think that it might very well be that Jack Smith welcomes a Florida jury because if there is a conviction, it will be much harder to say, ‘Well, that jury was somehow anti-Trump,’” said Stephen Saltzburg, a George Washington University law school professor and former Justice Department official.

Experts anticipate Trump’s lawyers to echo the former president’s public remarks by trying to get the case dismissed by arguing he was entitled to have the documents. Trump could also try to block prosecutors from being able to use key evidence, such as notes from his lawyer detailing conversations.

If the case gets to trial, experts said that Trump’s lawyers may attempt what is called “jury nullification”. That would involve convincing jurors that Trump should be acquitted, even if they believe Trump broke the law, because the violation was not serious enough to warrant charges.

“The theme of the defence can be riddled with suggestions of unfairness and selective prosecution — basically trying to convince a jury that even if the former president did what the government says he did, none of this should have ever ended up in a criminal prosecution,” said Robert Mintz, a defence lawyer and former Justice Department prosecutor.

Robert Kelner, a Washington criminal defence lawyer, said that, while an outright acquittal seems unlikely given the volume of evidence, a pathway for a mistrial exists if Trump lawyers can persuade even one juror to acquit on the grounds that the president enjoyed the absolute authority to declassify information.

That authority ended the moment Trump left the presidency, but even so, “some jurors will likely find it hard to rationalise convicting him for something that he previously had the absolute authority [to do] simply because he didn’t file the right forms and do it at the right time,” Kelner said.

In the end, facing a mountain of evidence and the prospect of years in prison, Trump’s best hope may be a tactic he often pursues: Delay, delay, delay. That’s according to Cheryl Bader, a former federal prosecutor and head of Fordham University Law School’s Criminal Defense Clinic.

“His best defence may be to try to ride out the election cycle, be elected as president and therefore be in charge of the Justice Department before the case goes to trial,” Bader said.