Paul Manafort’s trial in Alexandria, Virginia, captured most of the nation’s attention this week, but legal proceedings across the Potomac River in Washington may be the best indicator of where the Russia investigation is going next.

Special counsel Robert Mueller’s team questioned Kristin Davis, the so-called Manhattan Madam, before a grand jury at the D.C. federal courthouse on Friday. Mueller is reportedly probing her connections with veteran GOP political operative Roger Stone. Elsewhere in the building that same day, a federal judge held Andrew Miller, another Stone associate, in contempt of court for refusing to obey a grand-jury subpoena also issued by Mueller for his testimony.

It’s increasingly apparent that Stone, a political dirty trickster and occasional adviser to President Donald Trump, may be in serious legal jeopardy. Stone himself told NBC’s Meet the Press in May that he is “prepared” to be indicted by Mueller. In the interview, he suggested that the charges could be related to his business operations instead of Russian electoral interference. “It is not inconceivable now that Mr. Mueller and his team may seek to conjure up some extraneous crime pertaining to my business, or maybe not even pertaining to the 2016 election,” Stone told moderator Chuck Todd. “I would chalk this up to an effort to silence me.”

For what, exactly, would Mueller indict Stone? As with many things surrounding the Russia investigation, the answer isn’t quite clear. Two potential avenues are emerging from the witnesses that Mueller has already subpoenaed and the question that he’s reportedly asked them. If Stone is indicted on charges related to his super PAC or for other business dealings unrelated to foreign election meddling, the political impact could be minimal at first. If, on the other hand, the charges pertain to Russian cyberattacks, it would mark a major shift in the Russia investigation.

Mueller’s operations are largely hidden from public view, making it hard to gauge his progress in the Russia investigation. At the same time, he and his team appear to be taking a heightened level of interest in Stone’s activities. Mueller’s team has called at least a half-dozen Stone aides and confidants before the grand jury this year, often in addition to the more standard interviews with FBI agents. Stone has told reporters that he himself hasn’t been contacted by the special counsel yet, a silence that could indicate he is a target of the investigation.

This would fit Mueller’s pattern so far in the Russia investigation. A similar wave of grand-jury appearances preceded the first indictment of Paul Manafort and Rick Gates last October, as well as the guilty plea of Michael Flynn last December. Other targets had more conspicuous bullseyes on them. Manafort’s history of shady business practices had already raised suspicions long before Mueller’s appointment as special counsel. Flynn’s criminal liability was even more well known: Trump dismissed him from his post as national security advisor after it became public that Flynn had lied to FBI investigators about his conversations with the Russian ambassador a few months earlier.

One possibility is that Mueller is scrutinizing Stone’s business dealings, as Stone himself suggested might be the case. Stone began the 2016 election as an adviser to Trump when his campaign was still in its early stages. Trump severed formal ties with Stone in August 2015, describing him as a “publicity seeker” who “no longer serves a useful function for my campaign.” But Stone kept in touch with the eventual Republican nominee and served as an informal adviser throughout the election.

Stone also formed a super PAC named the Committee to Restore America’s Greatness, a pro-Trump organization that sought to aid his candidacy. Many of the Stone associates that Mueller has questioned have ties to the group. They include Jason Sullivan, a social-media specialist who worked for the group in the summer of 2016, and John Kakanis, who worked as Stone’s accountant and driver. Sullivan testified before a grand jury in June, while Kananis received a subpoena in May. The special counsel’s office is also reportedly probing Stone’s tax returns and other financial information.

Mueller has the legal authority to prosecute “any matters that arose or may arise directly from the investigation” under the orders given to him by Deputy Attorney General Rod Rosenstein, who oversees the Russia investigation thanks to Attorney General Jeff Sessions’s recusal from it. That means the special counsel can bring charges against Stone for any acts he discovers while investigating Russian collusion with the Trump campaign, even if those acts aren’t related to the collusion itself. Indeed, the most prominent figures prosecuted by Mueller so far—Manafort, Gates, and Flynn—all faced charges unrelated to the 2016 election.

A more dramatic possibility is that Stone could be indicted on charges related to Russian collusion itself. Sam Nunberg, another Trump campaign adviser, told Bloomberg in May that he turned over years of emails with Stone to the special counsel’s office, and that Mueller’s team questioned him about Stone’s relationship with WikiLeaks founder Julian Assange. Assange helped distribute documents stolen from the Democratic National Committee and the Hillary Clinton campaign by Russian military hackers, who adopted the persona of a Romanian hacktivist codenamed Guccifer 2.0. In July, Mueller indicted twelve Russians for election-related cyberattacks against Democratic Party organizations and candidates.

Stone was in communication with both Assange and Guccifer 2.0. He exchanged private messages with the WikiLeaks Twitter account on multiple occasions throughout the 2016 election, and at one point told Nunberg he had dined with Assange himself. (The veracity of that assertion is unclear.) Stone also told reporters last month that he was the unnamed person in communication with the Russian hackers behind the Guccifer 2.0 persona in Mueller’s July indictment. The extent and nature of these communications remains murky at best. Stone has repeatedly denied any wrongdoing, including collusion with the Russian government.

If Mueller indicts Stone on unrelated charges, as he has done with Manafort and Gates, it would widen the Russia investigation without deepening the legal and political peril for Trump himself. Indicting Stone on collusion-related charges, on the other hand, would mark a sea change for the inquiry itself. For more than a year, Mueller’s investigation has publicly avoided the question of whether Americans actively conspired with Moscow to subvert U.S. democracy. What has been conjectural and speculative until now could soon become all too real.