Over 25 years as an F.B.I. agent, Timothy R. Thibault reeled in big names while investigating public corruption, sending two Democratic congressmen to prison and overseeing sensitive inquiries into the Clinton Foundation and the former governor of Virginia, Terry McAuliffe, another Democrat.
But now as Republicans and allies of former President Donald J. Trump work to undermine federal investigations into the former president, they have trained their sights on the little-known Mr. Thibault, who played a role in opening the Justice Department’s criminal inquiry into Mr. Trump’s efforts to reverse his 2020 election loss. In their casting, Mr. Thibault, who retired last year, is the face of bias and misconduct at the bureau.
Powerful Republican lawmakers, including Representative Jim Jordan and Senator Charles R. Grassley, demanded that Mr. Thibault testify before their committees. Citing an anonymous G.O.P. official, Mr. Jordan’s panel in a news release last year denounced Mr. Thibault as “public enemy No. 1.”
But his story is more complicated than Republicans have made it out to be. As an investigator working on high-profile public corruption cases and international terrorism, he was well regarded, eventually rising to one of the most senior positions in the bureau’s Washington field office and winning internal awards for his professionalism.
But, in an atmosphere in which Republicans have been seeking evidence of anti-conservative bias within the F.B.I., he opened the door to intense scrutiny of his record. Republicans have cited several social media posts — including one that seemed to align him with critics of Mr. Trump — and his handling of a number of cases that touched on claims by Mr. Trump about election fraud and wrongdoing by the Biden family.
A number of current and former F.B.I. agents are siding with the Republicans in seeking to show bias inside the bureau. Some have even joined Mr. Jordan’s committee, including two former counterintelligence agents.
Another former agent — who now works for a conservative think tank and sought to solicit information from a right-wing author with links to a former White House strategist for Mr. Trump — appears to have leveled complaints against Mr. Thibault that Mr. Grassley has seized on.
The scrutiny of Mr. Thibault has its roots in his management of a public corruption squad that became mired in conflict, including over investigating Hunter Biden, another focus of inquiry by Republicans on Capitol Hill.
Mr. Thibault was thrust into the harsh spotlight of politics in May 2022, when Mr. Grassley released a letter addressed to the F.B.I. that accused him of partisanship.
The letter laid out his activity on social media, which included expressing support for articles critical of Attorney General William P. Barr and reposting an article in The Atlantic titled, “Donald Trump Is a Broken Man.” Mr. Grassley also accused Mr. Thibault of an anti-Catholic post on Twitter about pedophiles. (Mr. Thibault, responding to a Catholic priest denouncing abortion, wrote in his post, “Focus on the pedophiles.” Mr. Thibault’s friends say that he was raised Catholic.)
Mr. Thibault, his friends and former colleagues say, was an outstanding investigator who is not partisan but knows he displayed poor judgment on social media.
Mr. Thibault worked on many cases involving both parties, his former colleagues said. He was the primary agent who successfully investigated former Representative William J. Jefferson, a New Orleans Democrat, and Jesse L. Jackson Jr., a former Democratic congressman from Illinois. Both were convicted.
Former colleagues have also repeatedly acknowledged his work. In 2006, Mr. Thibault received an annual award recognizing “professional excellence” and “sterling character.” He also earned the attorney general’s award for distinguished service for his role in Mr. Jefferson’s case.
Mr. Thibault’s lawyer did not respond to emails seeking comment, but his lawyer’s firm provided a statement last year after Republicans singled out Mr. Thibault.
“He firmly believes that any investigation will conclude that his supervision, leadership and decision making were not impacted by political bias or partisanship of any kind,” the statement said.
The Office of Special Counsel is investigating whether Mr. Thibault’s posts violated the Hatch Act, which prohibits federal employees from engaging in political activities while on the job.
The F.B.I. declined to comment. Mr. Thibault could not be reached for comment.
After focusing on international terrorism from 2018 to 2020, Mr. Thibault returned as a top agent, handling criminal matters at the F.B.I.’s Washington field office.
There he clashed with three agents who served on a public corruption squad that fell under his supervision at an F.B.I. office in Manassas in Northern Virginia. Even before Mr. Thibault’s return, the members of the squad had been warned by their supervisor that because of previous troublesome comments by the agents, partisanship was unacceptable.
Under Mr. Thibault, the squad appears to have fractured over how to handle politically fraught cases.
In one instance, he rejected a request to open an investigation into whether Italian satellites had been used to alter votes in favor of President Biden, a conspiracy theory that Mr. Trump peddled, two former law enforcement officials said.
The Justice Department under Mr. Trump also believed the theory was baseless. When the White House pressed the department to investigate, the acting deputy attorney general, Richard P. Donoghue, derided it as “pure insanity.”
Mr. Thibault was also connected to another incident that has drawn attention from Republicans.
Before the election, two agents contacted Peter Schweizer, who is the president of the Government Accountability Institute, which has received millions of dollars from prominent conservative donors. Mr. Schweizer also writes for Breitbart, a right-wing news outlet, and had ties to Stephen K. Bannon, a former White House strategist for Mr. Trump.
In an interview, Mr. Schweizer confirmed that the two sought information about Hunter Biden, the president’s son, whose foreign business dealings have been the subject of intense Republican scrutiny for years.
Mr. Schweizer had recently published a book, “Profiles in Corruption: Abuse of Power by America’s Progressive Elite,” delving into the financial dealings of the Biden family. The agents, Mr. Schweizer said, wanted to know if he could share documents related to Hunter Biden’s foreign business ties that he might have gathered for his work. Mr. Schweizer said he passed on corporate records and other files.
After The New York Post reported on the younger Mr. Biden’s laptop in October 2020, Mr. Schweizer said he informed the F.B.I. agents that he had a copy of the laptop’s contents, which were circulating in right-wing circles. But even though the agents had expressed interest, Mr. Schweizer said they never followed up, and in the end, “I never sent anything to them.”
The relationship “ended abruptly without any explanation,” he added.
The two agents’ outreach to Mr. Schweizer caused tension among the F.B.I. officials in Delaware running the case, who had seized the laptop in late 2019 using a grand jury subpoena, the former officials said.
At least one of the agents was instructed by Mr. Thibault to shut down that line of inquiry because of concerns that Mr. Thibault had received in a classified briefing about the possibility of the laptop containing disinformation, one of the former law enforcement officials said.
In a news release, Mr. Grassley accused Mr. Thibault of “improper conduct” in the investigation into Hunter Biden. Mr. Trump, for his part, lashed out on social media, claiming Mr. Thibault had been involved in “hiding and suppressing from the Public and the Media” the “Laptop from Hell,” before the 2020 election.
In his May 2022 letter to the F.B.I., Mr. Grassley tied Mr. Thibault to Bruce Ohr, a former Justice Department official, and his wife, Nellie Ohr, who were portrayed by Trump supporters as pro-Democratic conspiracy theorists out to destroy Mr. Trump. The three attended a seminar overseas in February 2016. One of the former law enforcement officials said Mr. Thibault did not know the couple.
A person familiar with the matter said one of the agents involved in the outreach to Mr. Schweizer, Thomas Olohan, had drafted a lengthy memo accusing Mr. Thibault of being biased against Mr. Trump. In the memo, Mr. Olohan suggested that the fact that Mr. Thibault and the Ohrs had attended the same seminar was evidence of bias on the part of Mr. Thibault.
The men had clashed after Mr. Thibault learned that Mr. Olohan’s daughter — who reports for The Daily Signal, a news site run by the conservative Heritage Foundation — had been writing about someone her father was investigating, two former law enforcement officials said. After Mr. Thibault took him off that case, Mr. Olohan transferred to another criminal squad before retiring last year.
Mr. Trump and his allies have vigorously attacked the F.B.I.’s reasons for opening the Russia investigation, trying to undermine its legitimacy.
And now Mr. Grassley has accused Mr. Thibault of improperly opening an investigation into Mr. Trump and his campaign. Mr. Thibault drafted a memo last spring that began the inquiry into efforts to create slates of electors pledged to Mr. Trump in states he had lost in 2020, according to the former law enforcement officials.
But under a policy established by Mr. Barr’s Justice Department in the months before the 2020 election, top F.B.I. and Justice Department officials need to sign off on the memo before investigating any candidate. The rule was meant to avoid influencing the outcome of the race.
Charlie Savage, Luke Broadwater and Jo Becker contributed reporting. Kitty Bennett contributed research.