– Long before the convictions last week of two former members of President Donald Trump’s inner circle, the political left’s expectations for the Russia investigation were at a fever pitch.

Democrats predicted that the special counsel, Robert Mueller, would break with a half-century of policy and prosecute a sitting president.

Mueller, a lifelong Republican who is an unlikely hero for the anti-Trump resistance, faces a series of crucial decisions in the coming months. Will he subpoena the president? Recommend charges? Will he write a public report? Each could help sway the midterm elections and shape the future of the presidency itself.

For insight on what he will do next, those who have known him for years say, do not look at the mythology that has built up since Mueller was appointed 15 months ago. Look instead to his four decades of government service.

As he advanced from line prosecutor to top Justice Department official to head of the FBI, his time was marked by aggressive prosecutions but also a deference at key moments to precedent, tradition and higher office. “He’s the last guy who’s going to do anything that’s even slightly a departure from the bedrock principles,” said Glenn Kirschner, who worked alongside Mueller as a homicide prosecutor.

The special counsel investigation has followed a familiar path, colleagues said, largely because Mueller, a publicity-averse 74-year-old, has stuck to his approach.

“He’s the same guy he’s always been,” said Marilyn Hall Patel, a retired federal judge in San Francisco. “Steady, measured, cautious.”

Shortly after taking over as U.S. attorney in San Francisco in 1998, former colleagues recalled, Mueller asked all the supervisors in the office to step down. He promptly sent a Justice Departmentwide e-mail announcing that “the following positions are now open” — and listing every major prosecution job in Northern California.

Many in the office found it brusque and off-putting. But Mueller told colleagues that he had learned a management style decades earlier as a Marine platoon commander: You cannot make people do things that they are incapable of doing. So rather than prodding employees, he preferred to move quickly to assemble the best possible team, even if it was disruptive.

As special counsel, Mueller has recruited talented prosecutors from across the country, stocking the office both with trusted longtime colleagues and younger prosecutors with sterling résumés. “If you have an opportunity to work with him and learn from him, you do it,” said Melinda Haag, who once served as Mueller’s chief white-collar prosecutor.

Mueller was not the obvious choice to lead the San Francisco office during the Clinton administration. Those jobs usually go to politically connected lawyers, and Sen. Barbara Boxer, D-Calif., had formed a selection committee to recommend candidates.

Mueller was tied to the wrong party, having served as a top Justice Department appointee of George H.W. Bush. But the San Francisco office was adrift, and career prosecutors at the Justice Department in Washington recommended Mueller. And though Boxer had an eye for liberal nominees who diversified the workforce, the chairwoman of her committee, Cristina Arguedas, had known and respected Mueller when he was a young prosecutor and she was a public defender.

As the nation’s top criminal prosecutor during the Bush administration, Mueller oversaw the high-profile investigations of the Lockerbie bombing, the prosecution of crime boss John Gotti and the sprawling BCCI financial corruption scandal.

Afterward, he took a sizable step down to return to front-line law enforcement. He became a homicide prosecutor in Washington, a city still reeling from the violence of the crack epidemic of the 1980s and early 1990s.

“I love everything about investigations,” he once said, reflecting on that period. “I love the forensics. I love the fingerprints and the bullet casings and all the rest.”

He demands the same from his subordinates, whom he expects to be steeped in the details. “The thing that would set him off was when someone would come in for a briefing unprepared,” said John S. Pistole, a former deputy FBI director.

By almost any measure, Mueller has led the swiftest, most successful independent investigation in modern Washington. In just over a year, he has indicted 25 Russians for trying to influence a U.S. election. He has won a conviction of Trump’s campaign chairman at trial and secured guilty pleas from two campaign aides and the former national security adviser.

Little precedent exists for the case Mueller has before him, but 50 years of Justice Department legal policy says that sitting presidents cannot be indicted. Congress, with its impeachment power, may prosecute a president, but the Justice Department may not.

So when Trump’s lawyer, Rudy Giuliani, announced that he had been assured that Mueller would abide by that policy, it rang true for those who have known Mueller for years.

“If the Department of Justice has a legal opinion that says you shouldn’t indict the president, he will feel like he has to follow that,” Arguedas said. “Because that’s his job. He’s not a guy who’ll say, ‘I don’t care about that legal opinion.’ ”

That may be why Mueller has allowed negotiations to drag on for months over whether Trump will sit for an interview. Forcing the issue with a subpoena would test the limits of executive power, and Mueller does not make such moves lightly.

Mueller has many options for ending his investigation, but Giuliani, the president’s lawyer, has said Mueller plans to issue a report on his findings, though the special counsel’s office has never confirmed that path. Any such report — especially a lengthy, damaging one like the one independent counsel Ken Starr released about President Bill Clinton — would raise the prospect of a spectacle in Congress.

But the independent counsel law that allowed for such a highly detailed report in the Clinton case expired, and under replacement Justice Department regulations, Mueller is required only to send a short, confidential summary of his investigation to the deputy attorney general, Rod Rosenstein.

A less splashy finale suits Mueller.

“He’s going to find out what there is to find out, and he’s going to say it in the most straightforward, neutral way possible,” Arguedas said. “And then he’s going to walk away, because his job will be done. He won’t go on any talk shows, and he won’t write a book.”