Few people have heard of Michael Horowitz, but that’s about to change.

Horowitz, the Department of Justice (DOJ) inspector general, is an increasingly critical player in the controversy surrounding the FBI, President Trump Donald John TrumpSchiff: Nunes gave Trump 'secretly altered' version of memo Davis: ‘Deep state’ existed in ’16 – but it elected Trump Former Trump legal spokesman to testify to Mueller about undisclosed call: report MORE and the Russia investigation.

With little fanfare, he has been conducting a sprawling probe of the FBI’s handling of the 2016 investigation into Hillary Clinton Hillary Diane Rodham ClintonDavis: ‘Deep state’ existed in ’16 – but it elected Trump Former Trump legal spokesman to testify to Mueller about undisclosed call: report WSJ: Agents' texts reveal McCabe knew of Clinton emails for at least a month MORE’s use of a private email server. His full report, which could set off shockwaves, is expected by the early spring.

A political appointee in both the Bush and Obama administrations, Horowitz’s yearlong investigation already reportedly contributed to the early resignation of Deputy FBI Director Andrew McCabe Andrew George McCabeMORE. And his work has been felt in other ways.

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Horowitz also uncovered a series of text messages between FBI officials Peter Strzok and Lisa Page that led special counselto remove Strzok from his team. Those texts have fueled accusations among GOP lawmakers that Mueller’s probe is tainted by partisanship.

Those who know Horowitz portray him as an independent voice.

“He is really one of the smartest and fairest people I have ever had the pleasure to work with,” said Bill Hamel, who served as assistant inspector general for investigations at the Department of Education. “He’s a straight shooter and a fair guy. He’s an honest broker.”

But Horowitz’s reputation will be put to the test when he releases the findings of the Clinton investigation. No matter what he concludes, it’s likely to create a political firestorm, coming at a time when both Republicans and the White House are charging that political bias is rampant at the Justice Department and at the FBI.

Horowitz attracted public attention early in his career as an assistant U.S. attorney in New York for prosecuting corrupt police officers in the infamous “Dirty 30” case in the mid-1990s.

He later moved to the Justice Department’s criminal division in Washington, where he served as chief of staff for a period spanning the Clinton and Bush administrations.

Bush later appointed Horowitz to a six-year term as a commissioner of the U.S. Sentencing Commission, an agency within the judicial branch that writes sentencing guidelines for federal courts. He was then selected by President Obama to serve as the Justice Department’s top watchdog in 2011.

His job is demanding. Horowitz oversees a department of nearly 500 employees who are responsible for investigating waste, fraud, abuse and misconduct within the Justice Department.

“You’re there to help the agency succeed in doing its job,” said Hamel, who has known Horowitz since his days working in New York. “They have to be independent to do that job. They can’t be swayed by political issues.”

He is best remembered in his current role for coming down hard on regional officials at Justice and the Bureau of Alcohol, Tobacco, Firearms and Explosives for the infamous “Fast and Furious” operation in which officials allowed the illegal sale of firearms in a botched effort to track Mexican drug cartels.

Just six months into the job, Horowitz issued a report eviscerating law enforcement officials in Arizona for a “significant lack of oversight” and disregard for “the safety of individuals in the United States and Mexico.”

While the investigation absolved Attorney General Eric Holder Eric Himpton HolderBill Maher: Trump’s tombstone will say ‘picked fights with black people’ Uber hires first-ever chief diversity and inclusion officer A law enforcement report card for Trump’s first year MORE of blame, Horowitz recommended that the Justice Department consider potential disciplinary action for 14 officials involved.

“It was just a remarkably intense first six months on the job. I know I wouldn’t have chosen to walk into the job that way. Looking back on it, it was sort of trial by fire,” Horowitz told The Washington Post in 2014. “You sink or you swim pretty quickly, and fortunately I didn’t sink. People can use their own judgment about how well I swam.”

Horowitz also clashed with the Obama administration over Justice and the FBI bucking requests for documents from the inspector general’s office.

Horowitz’s work has earned him respect among his peers. He has been twice elected to lead the Council of the Inspectors General on Integrity and Efficiency, the independent panel of inspectors general across the federal government.

“He is a man of the utmost integrity who is willing to call the shots as he sees them,” said Stanley Twardy, a Stamford, Conn.-based lawyer who has known Horowitz professionally since his days as a U.S. attorney.

Horowitz formally announced last January that he would investigate allegations of wrongdoing by Justice Department and FBI officials leading up the 2016 election, in response to demands from both Democrats and Republicans.

It’s possible that both parties will get political ammunition from Horowitz’s report.

The inspector general is examining whether then-FBI Director James Comey James Brien ComeyDavis: ‘Deep state’ existed in ’16 – but it elected Trump WSJ: Agents' texts reveal McCabe knew of Clinton emails for at least a month CNN: FBI agent Strzok helped write letter reopening Clinton probe MORE broke FBI procedure with his public disclosures about the Clinton case, including the letter that he sent to Congress a few weeks before the election. Before Trump fired Comey, Democrats were outspoken in their criticism of those decisions, saying they violated procedure and cost Clinton the election.

But Horowitz is also looking into allegations that McCabe should have been recused from the investigation. Republicans, including Trump, have seized on reports that McCabe’s wife accepted campaign contributions from Clinton ally and former Virginia Gov. Terry McAuliffe when she ran for state office in Virginia, calling it a clear conflict of interest.

Finally, Horowitz is also looking into unauthorized disclosures of information.

Lawmakers have pressed Horowitz to expand the scope of the probe to include Comey’s firing or Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsUS to prioritize new asylum applications over past filings California considers state-run bank for pot businesses Trump doesn't recognize foreign-born black and brown people as American MORE’s recusal from the separate investigation into Russian interference in the 2016 election.

Horowitz has not committed to looking into Comey’s firing, signaling that doing so could present a conflict with Mueller’s investigation.

Horowitz’s probe has become all the more relevant in light of McCabe’s decision to step down last week. According to The New York Times, Christopher Wray, whom Trump installed as FBI director last year after Comey’s ouster, had raised concerns about details of the forthcoming inspector general report that led him to propose that McCabe be demoted.

The Washington Post subsequently reported that Horowitz is examining why McCabe seemingly did not move forward for several weeks on a request to examine new emails in the Clinton investigation that were found on former congressman Anthony Weiner’s (D-N.Y.) computer.

“There are a lot of legitimate questions that I hope would be answered by this inspector and that probably aren’t going to paint the DOJ or the FBI in a particularly good light,” said Ron Hosko, a former official in the FBI’s criminal investigative division.

The findings could further play into GOP charges of political bias at the FBI, which critics view as part of a broader effort to inhibit Mueller’s investigation.

The text exchanges between Strzok and Page came to public light when the Justice Department delivered them to GOP-led panels in Congress in December and also reportedly allowed journalists to view them.

“These text messages prove what we all suspected: high-ranking FBI officials involved in the Clinton investigation were personally invested in the outcome of the election and clearly let their strong political opinions cloud their professional judgment,” House Judiciary Chairman Bob Goodlatte Robert (Bob) William GoodlatteSeveral lawmakers have seen intelligence behind Nunes memo Key senator floats new compromise for immigration talks Dem whip pushes back on 'four pillars' approach to Dreamers MORE (R-Va.) told Deputy Attorney General Rod Rosenstein Rod Jay RosensteinOvernight Cybersecurity: GOP, FBI clash over FISA memo | Uber breach under Senate scrutiny | Upcoming House cyber diplomacy hearing Trump asked Rosenstein about Russia probe, if he was on Trump's 'team': report Nunes fires back at FBI for 'spurious objections' to memo release MORE at a hearing in December.

The Justice Department came under fire from Republicans in January when lawmakers discovered a five-month gap in the text messages; Horowitz has subsequently said he recovered the missing exchanges and would provide copies to the department, which could decide to release them to Capitol Hill.

Horowitz told lawmakers last November that his investigators had reviewed roughly 1.25 million records and conducted dozens of interviews in connection with the ongoing investigation.

At the time, he said he expected the report to be issued by March or April.

Otherwise, the inspector general has remained tight-lipped on the status of the investigation, including the potential widening of its scope.

His statement last January contained an important caveat. “If circumstances warrant,” it said, “the [inspector general] will consider including other issues that may arise during the course of the review.”