Americans probably won’t ever learn exactly what’s happened inside those sessions. But as with past high-profile grand juries, the witnesses themselves could offer some small help. (Or perhaps even more, if they are as chatty with reporters as the leak-prone White House has been.) While prosecutors often ask witnesses not to discuss the proceedings, they are under no legal obligation to keep quiet.

With this in mind, I spoke with veterans of high-profile Washington investigations during the Bill Clinton and George W. Bush administrations about their experiences. Their memories could serve as a preview of what Mueller’s witnesses face, and what they might tell the world once their testimony is over.

The Clinton White House spent years wrestling with Independent Counsel Ken Starr’s wide-ranging probe, which began as an inquiry into a real-estate deal known as Whitewater and culminated in the president’s impeachment in 1998 for lying under oath about his relationship with Monica Lewinsky. Years later, in 2003, Bush administration officials were accused of leaking the identity of Valerie Plame, a CIA agent married to Iraq War critic Joseph Wilson. The Justice Department tapped special prosecutor Patrick Fitzgerald to investigate. His inquiry led to jail time for former New York Times reporter Judith Miller, who initially refused to testify in front of the grand jury, and to the trial and conviction of Scooter Libby, a top aide to then-Vice President Dick Cheney.

Investigations like these “are profoundly damaging to the good order and proper functioning of a working White House,” as Russell Riley put it in May. They serve as a grave distraction to all involved, whether inside or outside of an administration, keeping them from their normal work and chipping away at morale. Grand juries only amplify those stressors, and the experience of testifying still seemed fresh to some of the witnesses I talked to.

“Physically, you’re in a closed room,” said Sidney Blumenthal, a former senior adviser in the Clinton White House, who testified before the Whitewater grand jury in the 1990s. “There are no windows. You’re taken to an upper floor. You sit surrounded by grand jurors who are on tiers of seats, and you [sit] at a table next to a prosecutor who asks you questions.”

Among the first things they all mentioned was the isolation. Unlike a typical courtroom hearing, grand-jury interviews aren’t accessible to the public. A witness’s legal counsel can’t attend—a virtually unique absence in the American legal system—although they can sit outside the room and wait for their clients to emerge.

Mary Matalin, a longtime Republican strategist who testified in the Plame investigation, told me that while witnesses can ask for a break to confer with their lawyers outside, “it is discouraged, as the jury seems to interpret that as an implication of some complicity or guilt.”