The dramatic sacking of the FBI director has left a bespectacled 52-year-old most Americans have never heard of holding the credibility of the US justice system -- and possibly even its democracy -- in his hands.
Rod Rosenstein, a man more used to beavering away in obscurity over case law, has been thrust into the middle of one of the biggest US political upheavals in years by a three-page brief he wrote for President Donald Trump.
The former attorney for Maryland, who has served under five presidents, was only two weeks into his new job as deputy attorney general when he was asked to pen a legal opinion as to whether FBI director James Comey mishandled an inquiry into Democratic candidate Hillary Clinton's use of a private email server.
His brief report, saying Comey was wrong to have publicly announced he advised dropping the case -- a decision that rests with the attorney general -- was used by the White House to justify sacking the FBI chief just four years into his 10-year tenure.
The sudden dismissal sent shockwaves through Washington. Democrats pounced, accusing Trump of trying to use Rosenstein's report and his squeaky-clean reputation to neuter an FBI investigation into whether his aides colluded with Moscow to sway last year's election.
In an open letter to Rosenstein Thursday, the New York Times said his spotless record had been tarnished by Trump's decision, and the fate of the explosive probe now rested on his shoulders.
"At this fraught moment you find yourself, improbably, to be the person with the most authority to dispel that cloud and restore Americans' confidence in their government. We sympathize; that's a lot of pressure," the Times wrote.
White House spokeswoman Sarah Huckabee Sanders has pointed to bipartisan support for Rosenstein to play down criticism of Comey's abrupt dismissal.
Trump echoed that argument in an NBC interview Thursday -- while also insisting he always intended to fire Comey, undercutting the White House explanation that he acted on Rosenstein's advice.
"He's highly respected, very good guy, very smart guy, the Democrats like him, the Republicans like him," Trump said of the deputy attorney general.
"He made a recommendation but regardless of recommendation I was going to fire Comey."
Rosenstein's brief said the FBI chief had been "wrong" in his handling of the Clinton email case. But he added that "although the President has the power to remove an FBI director, the decision should not be taken lightly."
Born in Philadelphia -- where he attended the city's Wharton school, Trump's alma mater, before studying law at Harvard -- Rosenstein is seen as a hard-hitting straight-shooter, despite his mild, almost forgettable appearance.
He was part of the team investigating the so-called Whitewater scandal during Bill Clinton's presidency, and gained the trust of both sides for his integrity.
His successful prosecution of a senior government official during his 12-year tenure as Maryland's top law official sealed his reputation, and he was one of only three out of 93 Bush-era attorneys to be kept on by the Obama administration.
On the wall of his office in Maryland, next to a photo of his wife and two daughters, he kept a plaque that read, "Don't tell me what I want to hear. Just tell me what I need to know."
He is now under pressure from Democrats to appoint a special counsel to investigate allegations about Trump's Russia ties, something he did not rule out during his confirmation hearings.
Asked by senators if he might be ready to greenlight an independent prosecutor, Rosenstein said, "I am, when I determine it is appropriate based on policies and procedures of the Justice Department."
Following Comey's sacking, however, the top Senate Democrat Chuck Schumer argued that the furor had irreparably compromised Rosenstein, and that the appointment of a counsel should not be left in his hands.