Paul Manafort goes on trial July 31 in suburban Virginia, facing 16 counts related to filing false individual tax returns; 7 counts related to failure to file reports of foreign transactions; 5 counts of bank fraud conspiracy; and 4 counts of bank fraud. As if that weren’t enough to keep prosecutors and defense attorneys occupied, the federal judge supervising the case, 78-year-old T.S. Ellis III, is a hardliner known for keeping things on track. Ellis has already ordered attorneys from both sides not to mention special counsel Robert Mueller’s investigation into possible collusion between Russia and Donald Trump’s 2016 presidential campaign, or, with one possible exception, Manafort’s role in running that campaign.

Yet the trial could still provide important insights into the bigger, more explosive picture: the interactions between Trump’s campaign and Russian government operatives seeking to defeat Hillary Clinton. “Judge Ellis believes in courtroom control,” says Joyce Vance, a former federal prosecutor. "But witnesses sometimes say things you don’t expect, and defense lawyers, on cross-examination, can open a door to new subjects. And once that happens, the witness is entitled to say anything that’s responsive. So it’s entirely likely we will hear things that illuminate the larger work Mueller is doing.”

The most obvious avenue would be through testimony related to Stephen Calk, a Chicago banker and an economic adviser to the Trump campaign who loaned Manafort $16 million—and who may have been promised a job in the Trump administration in return. (A spokesperson for Calk has denied any quid pro quo.) Five other bankers have been granted immunity to testify at Manafort’s trial. “I think we will undoubtedly hear from some of these bank folks that they were interested in good relations with Manafort because he was running the Trump campaign,” Vance says.

Whether good old-fashioned Washington influence-peddling connects to Russia’s influence campaign is the crucial question. “There is no part of Manafort’s financial shenanigans that is not fully on display to Mueller,” a congressional investigator says. “And Manafort doesn’t do things for free. So if your theory of the larger case is that Manafort was the hub of the collusion wheel—and if he got paid for helping facilitate these things—Mueller may have the records. Would they come in during this trial? We’ll see.”

Manafort has pleaded not guilty to all charges, and repeatedly said he knows nothing of Russian connections to the Trump campaign. Beyond the specifics of the charges, however, the trial will provide a fuller picture of the man who was a major force inside the Trump campaign for nearly three pivotal months in 2016, one that will be part of the mise-en-scène going forward. “Actually, I don’t think there is going to be a trial,” former federal prosecutor Juliette Kayyem says. “I think Manafort is going to do a night-before-trial plea. But assuming it does go forward, I don’t think there’s going to be a light bulb, eureka moment that gives us greater transparency about what happened with Trump and the Russians. I think to the extent the trial is about a corrupt enterprise, of which Manafort is a key player, it will have an impact on the atmospherics for any future trials related to the direct Trump issues.”

Jim Himes, a Democratic congressman from Connecticut, has spent months examining those issues as part of the House Intelligence Committee. “It is probably true that the crimes that Manafort has been charged with are separate and apart from any role he might have played during the campaign,” Himes says. “The intriguing thing, of course, is that he has all kinds of relationships with all kinds of Russians. This all sort of started with Manafort . . . and from the start, just about everybody associated with the Trump campaign has been lying about just about everything. The two guilty pleas, so far, are for lying to the F.B.I. The president regularly lies. This is an environment where nobody has any credibility in their public statements.”

Which is part of what gives the upcoming trial, with witnesses under oath, such weight. The verdict will be most directly important to Manafort, of course. But Mueller and his prosecutors have a great deal on the line as well. It is the first real test of the special counsel’s work. If Manafort is found not guilty on all counts, it could weaken Mueller’s hand for his second prosecution of Manafort, on charges including failing to register as a foreign lobbyist, in a Washington, D.C., court in September. And if Manafort walks this time, Trump would probably assail the “witch hunt” in a tweet storm whose force would rival Hurricane Katrina. “A majority of Americans have at least a raised eyebrow about Trump’s campaign. That eyebrow gets raised a lot more if his former campaign manager goes to jail,” Kayyem says. “I don’t think the stakes could be higher.”