Updated on August 2 at 9:23 p.m.

Special Counsel Robert Mueller has begun to issue subpoenas in his investigation into Russian interference in the 2016 election, according to several reports, the latest sign his investigation is moving quickly.

The Wall Street Journal first reported the story, saying Mueller was using a Washington, D.C.-based grand jury. Reuters confirmed the Journal report, and also said grand-jury subpoenas have been issued related to a June 2016 meeting at Trump Tower in which Donald Trump Jr., the president’s son-in-law Jared Kushner, and then-campaign chair Paul Manafort met with a woman they were told was a “Russian government lawyer” offering damaging information about Hillary Clinton. It was not immediately clear if the subpoenas came from the Washington grand jury.

The New York Times reports that Mueller has issued subpoenas through standing grand juries in Washington, rather than calling his own special grand jury for the case. Some of the subpoenas are tied to fired National-Security Adviser Michael Flynn, the Times reported.

A spokesman for Mueller declined to comment to the Journal, and President Trump’s attorney, Ty Cobb, said he was unaware of a grand jury but welcomed any steps that brought the investigation closer to its conclusion. That’s somewhat different than Trump’s previous statements. The president has called the investigation “the single greatest WITCH HUNT in American political history.”

Separately, CNN reported that Mueller’s probe has now expanded well past the 2016 election. “Sources described an investigation that has widened to focus on possible financial crimes, some unconnected to the 2016 elections, alongside the ongoing scrutiny of possible illegal coordination with Russian spy agencies and alleged attempts by President Donald Trump and others to obstruct the FBI investigation,” the report said, adding that investigators were combing over Trump’s business empire.

The CNN report adds detail to earlier reports from the Times and Bloomberg that the probe had widened to look at potential financial crimes. Mueller is said to be investigating whether the Trump campaign colluded with Russia to interfere with the election, business dealings of Trump and his associates, and whether Trump obstructed justice by firing FBI Director James Comey, asking him to drop an investigation into Michael Flynn, and other moves.

Trump has threatened Mueller in an attempt to keep the investigation confined to the election. He suggested in an interview with The New York Times that he might fire Mueller if the probe moved beyond Russian interference. However, Mueller’s commission gives him broad latitude to pursue whatever crimes he comes across. If Trump tried to fire Mueller, it could set up a replay of the 1973 “Saturday Night Massacre,” in which President Richard Nixon fired the Watergate special prosecutor, though only after his attorney general and his deputy both refused to do so and resigned. The incident is known as the beginning of the end for Nixon. Republican senators have warned Trump against firing Mueller, saying it would produce a political catastrophe.

The news of a grand jury is perhaps less a surprise than the speed with which it was impaneled. It suggests that Mueller’s team has moved past an exploratory phase. A grand jury hears testimony about potential wrongdoing and decides whether to charge people with crimes. It allows a prosecutor to subpoena documents and to put witnesses under oath for testimony. Mueller has also rapidly expanded his team, hiring a slew of high-profile lawyers, including several with experience in money laundering, organized crime, bribery, and witness-flipping. He recently added Greg Andres, a partner in a prominent white-shoe New York firm, to his group.

While Mueller’s team has largely avoided leaks, it’s believed that his work will stretch well into 2018 if not later. But a grand jury meeting in Washington would add to the carnival atmosphere that already prevails around this White House. Proceeding would attract stakeouts as the press tried to determine who was testifying, as happened during the investigation into who in the Bush administration leaked the name of CIA official Valerie Plame. Nearly 20 years ago, in August 1998, Bill Clinton became the first and only sitting president to testify before a grand jury, and was ultimately impeached for lying in his testimony.

The veteran investigative journalist Murray Waas reported on Thursday at Vox that several top FBI officials were told they might be called to testify about potential obstruction of justice by the president, including Acting Director Andrew McCabe. “Two senior federal law enforcement officials have told me that the new revelations illustrate why they believe the potential case against Trump is stronger than outsiders have thought,” Waas wrote.

Deputy Attorney Rod Rosenstein named Mueller special counsel in May, in response to Comey’s firing and the emergence of memos that detailed conversations between Trump and Comey in which the president seemed to be pressuring Comey to drop investigations. Trump also told NBC News’s Lester Holt that he fired Comey over the Russia investigation. Rosenstein is acting attorney general for matters related to Russia because Attorney General Jeff Sessions recused himself after admitting he had not disclosed contacts with Russian officials to the Senate, and because the collusion allegations concern the Trump campaign, of which he was a part. Sessions’s recusal has become a point of friction between the president and attorney general, with Trump publicly criticizing him on several recent occasions, and saying he wished he had not nominated him.

Before Mueller’s appointment, a grand jury in Alexandria, Virginia, was already investigating Flynn, who lied to Vice President Mike Pence and possibly to the FBI about contacts with Russian Ambassador Sergey Kislyak prior to inauguration day. Mueller assumed control of that grand-jury investigation after his appointment.

Stephen Vladeck, a law professor at the University of Texas, told the Journal that the Washington grand jury was an indication that Mueller was pursuing an ambitious investigation. “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,” Vladeck said. “This suggests that the investigation is bigger and wider than Flynn, perhaps substantially so.”

For months, Trump steadfastly insisted that there was no evidence of collusion between his campaign and Russia. There were, however, unreported contacts between Russian officials and Sessions, Kushner, and Flynn; inquiries into contacts with Russian intelligence by Trump staffer Carter Page; an investigation Manafort’s finances and possible money-laundering; and several other threads.

In July, however, Donald Trump Jr. admitted to attending the June 2016 meeting at Trump Tower. Emails showed that Trump Jr. believed that Natalia Veselnitskaya, whom he met, was “Russian government lawyer” bearing damaging information about Hillary Clinton. The emails also stated that the Russian government backed Trump over Clinton. Trump Jr. replied, “If it’s what you say I love it.” But he now says it was not what was said, and that he received no information. (Trump Jr. initially offered misleading and incomplete reports about the meeting before Times reporting drove him to release the emails.)

Since then, Trump has adopted a new line of argument, which is that if the meeting constituted collusion, it was not illegal, and that anyone would have done so. So far, this defense has been offered only in the court of public opinion. Mueller’s grand jury may offer Trump or some of his aides and family members the chance to make it in a court of law as well.