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.