A senior FBI official accused by Republican lawmakers of stonewalling an investigation into the business dealings of President Biden’s son and manipulating other public corruption investigations has left the bureau and was escorted out of the building, according to multiple press reports.

An assistant special agent in charge at the bureau’s Washington headquarters, Timothy Thibault, is said to have resigned from the agency, though neither the FBI nor the Justice Department has confirmed the exact reason for his departure or offered any other comment on the matter. 

A 20-year veteran of the agency, Mr. Thibault was involved in several public corruption cases, including the ongoing investigation into Hunter Biden’s business dealings over the past several years and other inquiries into election interference by officials in the Trump administration after the 2020 presidential vote.

Mr. Thibault had been under fire from Senator Grassley, a frequent critic of the FBI, because of what the Iowa lawmaker called his “active public partisanship” on social media and interference in corruption investigations.

In a July 18 letter to Attorney General Garland and the FBI director, Christopher Wray, the senator said multiple whistleblowers had come forward to allege that Mr. Thibault’s partisanship “went much deeper than the inappropriate social media posts.”

“Thibault was able to open or approve, or cause to be opened or approved, investigations based on unsubstantiated or unverified statements sourced to biased media publications,” the letter stated. “In other instances, whistleblowers have reported that Thibault declined to open or approve investigations based on partisan objectives notwithstanding the existence of proper predication.”

“This double standard in the application of Justice Department and FBI policies has resulted in investigations opened in a manner appearing to benefit the political aims and objectives of a select few Justice Department and FBI officials,” Mr. Grassley told justice department officials.

In separate letters, Mr. Grassley has accused Mr. Thibault and other officials in the FBI of orchestrating a campaign to downplay Republican efforts to investigate the contents of a laptop owned by Hunter Biden that was retrieved from a repair shop in Delaware. The effort, the senator said, included attempts to “falsely attack our Biden investigation as advancing Russian disinformation.”

Mr. Grassley’s letter also singled out the director of the Election Crimes Branch within the justice department’s Public Integrity Section, Richard Pilger, who is said to be “deeply involved” in the decision to investigate the actions of the Trump campaign and its advisors after the 2020 vote.

“I remain very concerned that political bias by a select group of Justice Department and FBI officials has infected the Justice Department’s and FBI’s usual process and procedure to open and pursue high-profile and politically charged investigations,” the letter stated.

Asked about Mr. Thibault during a hearing on Capitol Hill recently, Mr. Wray said it was “troubling” that the agent “liked” certain anti-Trump messaging on social media outlets and that the agency would do its utmost to protect any whistleblowers who came forward to report wrongdoing.

Responding to Mr. Thibault’s resignation, Mr. Grassley reiterated his allegation that the agent’s partisanship undermined the work and reputation of the FBI.

“This type of bias in high-profile investigations casts a shadow over all of the bureau’s work that he was involved in, which ranged from opening an investigation into Trump based on liberal news articles to shutting down investigative activity into Hunter Biden that was based on verified information,” the senator said in a statement.