Rick Gates had a prime corner office in Trump Tower: on the 14th floor, the nerve center of the Republican candidate’s presidential campaign, overlooking Fifth Avenue. But if you listen to his former colleagues at the top of Trump’s staff, the fact that Gates occupied that rarefied real estate was something close to a fluke, and it was the only thing of remote significance about Gates’s presence in 2016. “He had some organizational skills,” shrugs one top Trump campaign strategist. “And he could translate what Paul Manafort wanted done. But you’ve got to remember they were only in charge for thirteen weeks and one day. A really short time. And once Paul left, Rick’s knowledge was zero. He was not on the plane after August. He had nothing to do with the transition. The only thing Rick maybe could have known was about vendor relationships.”

A second senior Trump strategist dismisses Gates’s weighty-sounding title, “deputy campaign manager,” as overblown, though he is willing to give Gates some modest credit as an operative. “He was essentially the super-scheduler on the campaign, making the trains run on time. He had no strategic role, but was important in terms of planning trips, organizing the calendar, and making sure the departments were talking with one another. Once Manafort left Rick was shipped off to some sort of R.N.C. limbo role.”

Robert Mueller, however, clearly has higher regard for Gates’s worth. That’s why the special counsel’s fifth and most recent cooperation agreement has Gates pleading guilty to financial fraud and lying to investigators. Gates could be extremely valuable to Mueller’s probe of Russian meddling in the 2016 election on two fronts. The first is what Gates knows directly about possible collusion between the Trump campaign and Russian agents. “Sure, Gates was deputy campaign manager for only a fairly short time—but think about all the stuff that happens while Manafort and Gates are running the campaign,” says a lawyer who is part of one of the Congressional investigations. “The R.N.C. platform suddenly changes to become more pro-Russia. Carter Page flies to Russia. George Papadopoulos is giving interviews all over the world talking about there’s something really big coming. And the Russians are trying to approach the campaign with the hacked e-mails.”

At the top of Mueller’s list of questions to Gates, no doubt, is the June 9, 2016, meeting at Trump Tower that brought together Kremlin-connected lawyer Natalia Veselnitskaya, former Soviet counterintelligence officer Rinat Akhmetshin, Jared Kushner, Donald Trump Jr., and Manafort. “What did Manafort tell Gates about the Trump Tower meeting beforehand? What did he tell him afterward? I would also want to know if Gates was aware the hacked e-mails were coming,” the Congressional investigator says. “I don’t think there’s anything that Manafort does during the campaign that Gates doesn’t know about. Look at how close they were: the whole reason there’s a paper trail for the alleged money-laundering is because Manafort could not figure out how to open a PDF and edit it, so he keeps e-mailing it, Gates saying, ‘can you convert this to a Word document so I can falsify some numbers?’”

Manafort has consistently and vehemently denied any wrongdoing. But there is no refuting the breadth and depth of his professional relationship with Gates, which stretches back more than 20 years. Manafort was the idea man and the salesman; Gates was the mechanic, attending to the details of multi-million-dollar political and real-estate deals. And it’s here that Gates could be of the greatest use to Mueller, helping the special counsel increase the pressure on Manafort to flip. “Gates is close with the person on the campaign who had the deepest ties to Russia and Eastern Europe both politically and financially,” says California Democrat Eric Swalwell, a member of the House Intelligence Committee. “I haven’t seen any financial links that Trump and Manafort shared to Russia. What I do think they share is a pro-Russia history. I want to know if Gates says anything about that affinity factoring into anything like changing the convention platform. The campaign also had an eagerness for dirt on Hillary Clinton, and it didn’t care if that meant working with Russia. Russia wanted the sanctions to go away, if nothing else. Mueller wouldn’t strike a cooperation agreement with somebody who couldn’t tell him anything he didn’t already know.”

The 37-page indictment that gave a mighty push to Gates’s cooperation alleges multiple complicated international transactions. It also paints a painful picture of his dynamic with Manafort, in anecdotes that support the view of Gates as a mere flunky: in one episode, Gates takes the rap for Manafort’s overdue $300,000 American Express bill, so that his boss can tidy up a credit score and collect $16 million in loans. Manafort seems to still view Gates as his lackey: when Mueller released the cooperation agreement, Manafort issued a sneering statement saying, “I had hoped and expected my business colleague would have had the strength to continue the battle to prove our innocence.” This may be the first time in their relationship that the underling has the upper hand.