Former special counsel Robert Mueller's scheduled hearings before the House Intelligence and Judiciary committees on Wednesday should be among the most important moments of the Trump presidency—the rare, and perhaps only, chance to question the man who has spent two years investigating and uncovering the various attempts of Donald Trump and others to corrupt and circumvent American democracy.

Let’s be clear about what Mueller found. His work uncovered two separate criminal conspiracies that benefited the surprise election of Donald Trump. The first was allegedly led by Trump himself alongside his lawyer Michael Cohen, to cover up damaging stories about himself through federal felony campaign finance violations; the second, which Mueller literally charged as a “conspiracy against the United States” was led by the Russian government and involved a variety of pro-Trump, anti-Clinton information operations, advanced through identity fraud, computer hacking felonies, and other crimes. There is ample—even overwhelming—evidence that Trump sought to obstruct the Russia investigation.

Both conspiracies represent attempts to thwart the democratic practice of free, open, and transparent elections.

It’s important that Democrats keep the focus of Wednesday's hearing on that core message, because GOP members have made clear they plan to muddy Mueller’s findings—and his reputation—by shouting a lot about Peter Strzok, Lisa Page, Christopher Steele, and other vague, conspiratorial allusions and theories that ultimately matter not at all to Mueller's central findings.

Robert Mueller will pose a challenge to even the Democrats on the panel: a friendly but uncooperative witness, more prone to silence and deflection than the verbosity of a James Comey. Many, including some of his former Justice Department colleagues, hope the former special counsel will break with tradition and be blunt.

As someone who has followed Mueller closely for a decade, written a book on his time at the FBI, and read or watched almost every minute of public testimony or statement he's given, I can tell you it's not a great bet to rest the fate of US democracy on an unambiguous statement from Robert Mueller—particularly on the obstruction issue. Instead, Democrats will need to structure their questioning carefully, which requires a thorough understanding of the man at the witness table. To help guide that thinking, I have outlined below a series of key principles to know, as well as various questions and areas of inquiry to ensure the maximum impact of his testimony.

Please note: This guide is designed for serious, thoughtful members of Congress interested in the rule of law and preventing foreign interference in the elections. That means Mark Meadows of North Carolina and Jim Jordan of Ohio, you can stop reading now.

Mueller 101

The former special counsel is better at this than you are. Robert Mueller has been a prosecutor for more than 40 years, longer than all but one member of these committees has been in Congress. He spent decades questioning and cross-examining witnesses for a living, murder-boarded scores of cases with fellow prosecutors, and torn apart the intellectual weaknesses of countless “pros memos," the memos prosecutors write to justify charges. Aides at the FBI always described briefing him as if they were under cross-examination themselves. Given that Mueller has appeared before Congress more than 60 times, he’s almost certainly answered more questions from legislators than the members grilling him have ever asked themselves.

Mueller doesn’t care about what you care about. Aides at the FBI knew to never mention the word “legacy” around him. He’s not likely to be particularly concerned about how he comes across in the hearing, nor is he worried about the Twittersphere judging him or his report. Spending two years as special counsel—the central figure in the most watched, most anticipated investigation and political scandal in modern times—is, as I’ve previously noted, probably no more than the third hardest job Robert Mueller has ever had, after leading men in combat in Vietnam, and leading the FBI in the wake of 9/11.