The Justice Department’s Russia probe, which Donald Trump has dismissed as a “witch hunt” and “fake news,” is about to become very real. Special counsel Robert Mueller, who has been assembling a legal dream team to investigate Trump and his associates, has reportedly impaneled a grand jury in Washington, D.C., according to multiple news outlets, in the first major step toward possible indictments in the 2016 Russian election interference scandal.

While assembling a grand jury does not indicate that Mueller is necessarily preparing criminal charges, The Wall Street Journal reports that the move will expand his ability to call witnesses and place them under oath, issue subpoenas, and seek indictments, marking the beginning of a serious new phase in the Trump-Russia probe. According to Reuters, grand jury subpoenas have been issued in connection with last summer’s now-infamous Trump Tower meeting between three of the president’s top campaign advisers—his son Donald Trump Jr.; son-in-law Jared Kushner; and then-campaign manager Paul Manafort—and several Russians who were said to be peddling damaging information about Hillary Clinton as part of a Kremlin effort to aid Trump’s campaign.

The grand jury will be a powerful new tool for Mueller as his investigation reportedly expands to include financial dealings by the president, his company, and his associates. As D.C. trial attorney William Jeffress, who represented Scooter Libby, told me, prosecutors use grand juries to subpoena documents like e-mails connected to the allegations. “As a result of that investigation—which is a phase done by the F.B.I.—they will decide whether to take witnesses before the grand jury.”

Some components of this second phase are already underway. Hours after Trump unexpectedly fired F.B.I. Director James Comey in May, CNN reported that a separate grand jury in Alexandria, Virginia, had issued subpoenas seeking business records from associates of Mike Flynn, Trump’s former national-security adviser who resigned earlier this year. This suggests that the scope of Mueller’s investigation has also widened. “This is yet a further sign that there is a long-term, large-scale series of prosecutions being contemplated and being pursued by the special counsel,” Stephen Vladeck, a law professor at the University of Texas, told the Journal. “If there was already a grand jury in Alexandria looking at Flynn, there would be no need to reinvent the wheel for the same guy. This suggests that the investigation is bigger and wider than Flynn, perhaps substantially so.”

Trump has yet to comment on the news. “Grand jury matters are typically secret,” Ty Cobb, who serves as special counsel to the president, said in a statement to the Journal, adding that he was not aware that Mueller impaneled a second grand jury. “The White House favors anything that accelerates the conclusion of his work fairly. . . . The White House is committed to fully cooperating with Mr. Mueller.”