In such cases, a 1980 federal law known as the Classified Information Procedures Act is supposed to balance the government’s interest in maintaining secrecy with a defendant’s right to a fair trial. CIPA will be key as the DOJ prosecutes Trump, experts on national security law told POLITICO.

Here’s how it works.

‘Tense’ negotiations

Before the Justice Department brings a case involving classified materials, its prosecutors usually confer with intelligence officials at the agencies that own the relevant secrets. For instance, if a defendant allegedly stole classified analysis of a spy satellite’s photos, prosecutors would get in touch with officials at the National Geospatial-Intelligence Agency. They would tackle a dilemma: Just how much of that analysis could be included in open court?

The prosecutors would want to reveal as much as they needed to get a conviction, while the intelligence officials would likely urge caution. So the two sides negotiate, trying to decide just how far to go.

“There could be tensions,” said Gregory Gonzalez, a former prosecutor in the Justice Department’s National Security Division who handled cases related to classified material. “They’d be respectful conversations, but they’d be tense.”

Carrie Cordero, a national security lawyer who held senior positions at the Justice Department and the Office of the Director of National Intelligence, said she’s sure these talks shaped the contents of the Trump indictment.

“They likely selected documents that they knew they would be able to use throughout the case,” she said, referring to prosecutors.

In grand jury proceedings — which, unlike trials, are held in secret — prosecutors vaguely characterize the documents that were allegedly compromised, according to Gonzalez, now a partner at the law firm Wilkinson Barker Knauer. Grand jurors don’t get security clearances, and therefore they don’t get much detail.

The Trump indictment, for instance, included short descriptions of 31 documents he allegedly refused to return to the government after he left the White House. Various documents concerned “nuclear capabilities of a foreign country,” “military attacks by a foreign country” and “military contingency planning of the United States,” according to the indictment.

Protective orders and security clearances

Once an indictment is issued, the defendant’s Sixth Amendment right to a public trial comes into play. The Supreme Court has held that at least some pretrial proceedings — including evidentiary hearings and jury selection — are covered by the amendment’s guarantee.

Prosecutors typically move for a pretrial conference behind closed doors with defense attorneys and the judge assigned to the case. At the conference, government lawyers aim to educate the judge about the issues at stake and how they hope to handle the relevant classified material. In districts that commonly handle national security cases, judges may already have detailed knowledge of the complexities they’ll face. But the judge presiding over Trump’s case, U.S. District Judge Aileen Cannon, who has been on the bench for less than three years, doesn’t appear to have heard any cases involving classified material, according to a review of her career as a federal judge.

In this same pretrial period, any defense lawyers who don’t have security clearances will need to get them. The FBI’s background check process can take many months, so if prosecutors worry about excessive delays, they can urge the FBI agents to speed things up. Defendants can also try to find lawyers who are already cleared.

“Usually when you have cases involving classified information, there’s sort of a small bucket of defense lawyers who handle that because they either already have clearance or they had it and can get it quickly renewed,” said Sid Kamaraju, a former federal prosecutor in New York who prosecuted a former Central Intelligence Agency software engineer for causing what was at the time the largest theft of classified information in the agency’s history.

Federal judges don’t need clearances, and they undergo deep FBI background checks before their Senate confirmation. Their law clerks, however, are required to obtain security clearances when handling a case involving classified material.

Viewing evidence in a SCIF

Then it’s on to discovery, and the government starts sharing information with the defense. CIPA requires the judge to issue a protective order covering classified information so that defense attorneys could face legal consequences if they leak anything. In sealed proceedings, prosecutors and defense lawyers hash out just how much classified material will see the light of day, with the judge making the final decision. Descriptions, excerpts, and summaries of classified documents could all be revealed.

During discovery, according to Gonzalez, defense lawyers typically seek much more information than prosecutors offer. But since materials are classified, he added, they don’t have the full scope of what the documents say. They may use their clients’ recollections of the materials at hand — or even their own intuition — to seek details beyond what DOJ volunteers.

Once classified documents are determined to be included in the discovery material, defense lawyers can view the classified materials in a sensitive compartmented information facility, or a SCIF. The Miami courthouse where Trump was arraigned doesn’t have one, according to a person familiar with the facilities granted anonymity to discuss the sensitive location. But another building in the same complex does have one.

One factor that will likely make Trump’s case less complicated than many other Espionage Act cases is that, unlike most defendants in such cases, he isn’t detained pending trial, and therefore prosecutors wouldn’t need to find a way for him to view classified material while he is incarcerated, to the extent he would be allowed to see it. Trump may be able to view the material in a SCIF, like his lawyers.

The threat that some classified evidence would have to be revealed publicly at trial can sometimes give defendants extra leverage in plea talks.

“That’s exactly what CIPA was created to prevent, to prevent what they call graymail,” Gonzalez said, “your defense being that you’re going to expose this information.”

CIPA governs how defense attorneys can seek to reveal classified material in court. If the judge decides that the defendant and jury need more material than the DOJ wants to share, the government may need to drop some counts or move to have the case dismissed altogether. In Trump’s case, Cannon’s pretrial rulings on these sorts of disputes could dramatically affect the direction of the case.

Competing interests at trial

The highest hurdle in the process is getting classified material into a form in which jurors can see it, since they don’t get security clearances and since the default at trial is for evidence presented to jurors to be made public.

“The jury has to receive all of the evidence, so there are ways at trial where the jury gets to see the information, but it’s not necessarily made public,” Kamaraju said.

The Supreme Court has held that a judge can shut off public access to portions of a criminal trial only if the judge finds that closure is “narrowly tailored” and “essential to preserve higher values.”

One option is to load the material onto a dedicated, secure laptop that doesn’t have internet access and show it to the jury while sealing the courtroom (and later, redacting the transcript of the court proceedings). Another is to introduce substitute documents that use redactions or summarize the contents of the classified material without disclosing the most sensitive information.

The way the material is shown to the jury is often the subject of intense and protracted pretrial litigation. “Any case involving the use of classified information as evidence makes the case more complex and can potentially make the pretrial process take longer,” Cordero said.

At trial, according to Gonzalez, CIPA provides a “safety valve” that lets prosecutors object if they fear defense lawyers are going to reveal classified information that hasn’t already been approved. “That allows the government to object and request a decision from the judge if classified information is going to be elicited that has not otherwise been approved by the judge as part of the CIPA proceedings,” Gonzalez said.

CIPA also allows for witnesses — intelligence officers, for instance — to testify anonymously in some situations, Gonzalez said. That’s because, in national security cases, adversaries could seek to glean intelligence from court proceedings.

But some of these trial remedies, like the use of anonymous witnesses and substitute documents, may implicate another constitutional right: a defendant’s Sixth Amendment right to confront witnesses and challenge evidence.

“In cases that involve sensitive national security information, adversaries will surely be interested in trying to gather information from the public record,” Gonzalez said. “And so you don’t want to give too much away in public documents.”

“Even less-than-sophisticated actors in this space know that there’s a lot of public information that comes out in criminal proceedings,” he added.