While the White House busies itself with next month’s midterm elections, the Justice Department investigation into the Trump campaign’s ties to Russia appears to be quietly accelerating. In the nearly five weeks since he pleaded guilty, CNN reports that Paul Manafort has become a frequent guest of Robert Mueller, visiting the special counsel’s office in downtown Washington, D.C., no less than nine times since cutting a deal last month to aid Mueller’s probe in exchange for a reduced set of charges. Each day, according to the report, Manafort has pulled up at Mueller’s nondescript headquarters in a black Ford S.U.V.; based on the time he typically leaves, each session lasts about six hours.

While the exact nature of these conversations remains a mystery, it is believed Mueller is interested in a number of critical episodes that occurred while Manafort led Trump’s campaign through the G.O.P. nomination. Perhaps most notable is the infamous June 2016 Trump Tower meeting between Manafort, Donald Trump Jr., Jared Kushner, and a Kremlin-connected Russian lawyer. One source familiar with the matter told CNN that prosecutors have questioned Manafort—who worked for many years as a consultant for a pro-Russian political party in Ukraine—about his contacts with Russia. Other sources told ABC News that Mueller has been asking Manafort about his former business partner Roger Stone, a longtime Trump confidant who communicated with WikiLeaks and the Russian hacker Guccifer 2.0 during the campaign regarding the release of e-mails stolen from the Clinton campaign.

Stone dismissed the notion that Manafort, whom he has known for decades, will provide any damaging information to prosecutors. “I am highly confident Mr. Manafort is aware of no wrongdoing on my part during the 2016 campaign, or at any other time, and therefore there is no wrongdoing to know about,” he told ABC. “Narratives to the contrary by some in the media are false and defamatory.” And yet, for weeks Stone has signaled that he’s resigned to the possibility that Mueller will indict him. According to ABC, nearly a dozen Stone associates have been questioned by the special counsel, and a number have also appeared before a federal grand jury. “It’s not outside the realm of possibility” that Mueller “may consider bringing some offense against me,” Stone acknowledged in an earlier interview with ABC.

Nor is Manafort the only Trump alum who is unburdening himself to the special counsel. CNN reports that both Rick Gates, Manafort’s deputy and longtime business associate, and Mike Flynn, Trump’s former national security adviser, have met with the special counsel since pleading guilty. As my colleague Emily Jane Fox first reported, Trump’s former lawyer and fixer Michael Cohen has also met with federal investigators, providing more than 50 hours of information relevant to the Mueller inquiry and to the Southern District of New York.

Despite the flurry of activity, the Mueller probe has been publicly muted as midterms approach, with the special counsel hewing closely to Justice Department guidelines that stipulate prosecutors should avoid taking any major steps close to elections. Mueller will reportedly release his findings shortly after midterms, though it remains unclear whether that will mark the end of the investigation. There are growing expectations in Washington for Mueller to drop a large-scale indictment—one that could strike closer to home for Trump—once ballots are cast. And notably, Mueller’s team is still locked in negotiations with Trump’s lawyers about the possibility of a presidential interview: CNN reported last week that Trump’s legal team is preparing answers to written questions related to whether the Trump campaign colluded with the Russian in 2016. When asked if he would be willing to sit for an interview with Mueller, Trump told the Associated Press Tuesday, “You know that’s in process. It’s a tremendous waste of time for the president of the United States.”