Senator Mark Warner laughs, loudly. Hours earlier he’d met with Robert Mueller, the special counsel investigating the Trump-Russia affair. Had Mueller seemed intimidated by the president floating the idea of firing him? Warner, the leading Democrat on the Senate Intelligence Committee, finally collects himself. “I’m not going to talk about any of the subjects of our conversation,” he says, bursting into chuckles again. Five minutes after Warner hangs up, his non-answer answer is essentially confirmed by The Washington Post, which breaks the news that Trump himself is now under investigation by Mueller. So much for the president’s brushback pitch scaring the special counsel.

Which doesn’t, of course, mean that Trump won’t follow through and actually dismiss a man who insists on conducting an independent investigation, as he did F.B.I. Director James Comey. But for now, at least, Mueller has moved to center stage in this drama.

Not by choice, or by personality, however. “He’s apolitical, he hates publicity, he’s no flash and all substance,” says Peter Zeidenberg, a former federal prosecutor who worked the Valerie Plame investigation under President George W. Bush, and before that as a homicide prosecutor under Mueller. “Bob is not really a fun guy.” Zeidenberg illustrates the point by describing a party Mueller once threw. Mueller told his guests that the festivities would end promptly at 10 P.M. It was a beautiful summer Friday night, and dozens of staffers were drinking beer in the boss’s backyard, so Zeidenberg shrugged off the statement. At 10:05, Mueller shut off all the lights.

Where Mueller is heading next with the Trump-Russia investigation is almost as clear as that curfew. One sign is his top hires for the investigation staff. Michael Dreeben, an expert in criminal law, has been the No. 2 official in the solicitor general’s office, and he has argued (and lost) a major obstruction of justice case before the Supreme Court.

The obstruction probe will likely move the most quickly. Dan Coats, the director of national intelligence, and Mike Rogers, head of the National Security Agency, refused to publicly tell Senate Intelligence Committee investigators whether Trump had asked them to help squelch Comey’s queries. Both have agreed to answer questions from Mueller’s investigators. The next major turning point will be whether Deputy Attorney General Rod Rosenstein recuses himself from the Russia investigation. If he does, that means Mueller has called Rosenstein as a witness to Trump’s role in the firing of Comey.