Just when you thought you were keeping straight all the previously obscure government lawyers who might decide the fate of the republic, here comes Michael Horowitz, the inspector general for the Department of Justice. Republican Congressman Devin Nunes has dominated headlines for weeks with his controversial memo. But there is greater significance—and uncertainty—attached to Horowitz’s examination of the F.B.I.’s pivotal role during the 2016 presidential campaign. “His report will be more credible than the Nunes memo,” says Benjamin Wittes, the co-founder of the blog Lawfare. “Let’s just say Michael Horowitz is not a clown. And you’re talking about a situation inherently less susceptible to the foolishness that gave rise to the Nunes memo.”

Horowitz has tackled one high-profile mess previously. In 2012, less than six months after he’d arrived in the inspector general job, Horowitz issued a 471-page report on “Fast and Furious,” the undercover operation that was supposed to crack down on illegal gun trafficking but somehow lost track of 2,000 firearms—one of which was used to kill a Border Patrol agent. Horowitz’s report referred 14 officials for disciplinary action, but essentially exonerated then-attorney general Eric Holder of wrongdoing. “Michael is very cautious,” says Steven Cohen, who was a prosecutorial colleague of Horowitz’s in New York’s southern district of the U.S. Attorney’s office. “He’s dogged. He’s the opposite of a guy seeking to have a life in the limelight.”

There is no avoiding it this time. Horowitz’s probe has been lurking in the background since last January. He has quietly interviewed dozens of witnesses, including former attorney general Loretta Lynch and former F.B.I director James Comey. Horowitz was pulled into the headlines recently, though, when his office recovered missing texts between F.B.I. agent Peter Strzok and bureau lawyer Lisa Page. Then, in a preview of how his finished report will become a flashpoint, Horowitz’s lines of questioning were used to put an ominous spin on the ouster of F.B.I. deputy director Andrew McCabe.

The problem for both sides is that when Horowitz actually does announce his appraisal it will be grounded in facts and reality. “He’s generally considered to be a straight-shooting guy, though he likes to mind his congressional politics,” says Matthew Miller, a Justice Department spokesman under Holder. “Whether you agree with all his conclusions or not, Horowitz has a history of acting in good faith.” In 2003 George W. Bush chose Horowitz as a member of a federal sentencing commission. But Horowitz was appointed to his current role by Barack Obama. So if he turns up F.B.I. actions or actors that were prejudiced against Donald Trump, Democrats will have a hard time dismissing Horowitz as motivated by partisanship.

The process also lends impartiality: people criticized in an I.G. report are allowed to review the document in advance and to submit a rebuttal, which should have a disciplining effect on Horowitz’s analysis. It’s unlikely Horowitz will discover new and damning facts in a matter that’s been so thoroughly aired already. Instead, the report will have value as a comprehensive, on-the-record account of what went on at the highest levels of the Justice Department in 2016, as the Clinton e-mail investigation unfolded and the Russian hacking probe began.

That thoroughness will give the report weight—and could turn Horowitz’s conclusions, particularly his judgment of Comey, into potent weapons. If Horowitz is highly critical of the former F.B.I. director for breaking with precedent to publicly declare Hillary Clinton “extremely careless” in July, 2016, and of how Comey reopened the investigation in late October, again damaging Clinton’s chances, Horowitz would seemingly side with the Democrats.