President Donald Trump questioned the impartiality of the deputy director of the FBI, Andrew McCabe, who is planning to retire from the bureau in the months ahead after being buffeted by attacks over alleged anti-Trump bias in the agency.
In a tweet on Saturday, the president wrote: "How can FBI Deputy Director Andrew McCabe, the man in charge, along with leakin' James Comey, of the Phony Hillary Clinton investigation (including her 33,000 illegally deleted emails) be given 700,000 dollars for wife's campaign by Clinton Puppets during investigation?"
Mr McCabe spent hours behind closed doors on Capitol Hill this week being grilled by politicians on two separate committees as part of a new investigation of the FBI and its 2016 inquiry into Clinton's email practices when she was secretary of state.
His role supervising the email investigation has come under renewed scrutiny.
Mr McCabe's wife, Jill, received 700,000 dollars in donations from Virginia governor Terry McAuliffe's political action committee and the Virginia Democratic Party for a state Senate race in 2015.
The money was donated before Mr McCabe was promoted to deputy director and assumed a supervisory role in the Clinton email investigation. Mr McAuliffe is a longtime supporter of Mrs Clinton and her husband, former president Bill Clinton.
Mr McCabe became acting FBI director last May after president Trump fired Mr Comey, who was overseeing the bureau's investigation into Russian interference in the 2016 presidential election.
Mr Trump maintains there was no collusion between his campaign and the Russian government, and has blasted the investigation as a "witch hunt."
From his South Florida home, where he is spending Christmas, Mr Trump also tweeted that Mr McCabe "is racing the clock to retire with full benefits. 90 days to go?!!!"
Mr McCabe plans to retire in about 90 days, when he becomes fully eligible for pension benefits,The Washington Post reported on Saturday, citing people familiar with the situation.
Mr Trump and his Republican allies have made it clear that they want Mr McCabe out of the FBI. But Mr McCabe is a civil service employee who cannot be fired without clear evidence of wrongdoing.
Mr McCabe was among the candidates Trump interviewed for the FBI director's job after he dismissed Mr Comey. He also has been a focus of Mr Trump's ire for some time.
President Trump originally tweeted about Mr McCabe's wife's campaign in July, inaccurately describing the campaign donation as coming from Mrs Clinton: "Problem is that the acting head of the FBI & the person in charge of the Hillary investigation, Andrew McCabe, got $700,000 from H for wife!"
In a second tweet that month, the president asked "why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation," referring to Attorney General Jeff Sessions.
The FBI declined to comment on reports about retirement by Mr McCabe, who was summoned to Capitol Hill this week and grilled for hours by two congressional committees.
Republicans claim an anti-Trump bias exists in the bureau's ranks, citing the campaign donations to Mr McCabe's wife and, more recently, the release of hundreds of text messages between FBI counterintelligence agent Peter Strzok and FBI lawyer Lisa Page. Mr Strzok and Ms Page used words like "idiot" and "loathsome human" to describe Mr Trump during the campaign.