The barrage that the president and his allies have launched at the F.B.I. is focused on one small part of the mission — surveillance warrants — in an agency of 35,000 people that investigates everything from bank robberies to human trafficking to Wall Street malfeasance. But Mr. Trump could have more ammunition in the coming weeks as the Justice Department’s inspector general finishes a report widely expected to be critical of the F.B.I.’s handling of the final months of the investigation into Hillary Clinton’s private email server.
As part of that inquiry, Michael E. Horowitz, the inspector general, has uncovered text messages between two F.B.I. officials working on that case and also the Russia investigation in which they express intense dislike for Mr. Trump.
Mr. Horowitz is expected to reserve particularly harsh criticism for the two officials, Peter Strzok and Lisa Page. Conservative media outlets have already delivered their verdicts on the officials, who are regularly skewered on the popular Fox News program hosted by Sean Hannity.
Mr. Hannity recently described the Mueller investigation and decisions in 2016 by James B. Comey, the F.B.I. director at the time, as “one giant incestuous circle of corruption.”
Some Justice Department veterans see Mr. Horowitz’s report as another cudgel for those trying to discredit not only the Mueller investigation but also the wider law enforcement community.
“In this political atmosphere, anything critical of the F.B.I. will be used against it,” said Jack Goldsmith, a top Justice Department official in the George W. Bush administration.
Still, Republican lawmakers made a curious decision to focus so intensely on the government’s surveillance warrant for Mr. Page. Mr. Trump’s allies have spent more than a year distancing themselves from Mr. Page, and describe him as an insignificant foreign policy adviser who lasted only a few months on the campaign and never met Mr. Trump.
His trips to Moscow in 2016 were not connected to the campaign, they said, and campaign officials were unaware of his contacts with Russian intelligence operatives in 2013 when he was hired onto Mr. Trump’s foreign policy team during the election year.
The Republican memo, however, paints Mr. Page as the target of a political conspiracy that has the larger goal of hurting Mr. Trump — effectively binding Mr. Page and Mr. Trump more closely together in the public’s mind.
The memo also reveals that the surveillance warrant involving Mr. Page was renewed on multiple occasions, including during the Trump administration, meaning that top law enforcement officials had convinced the Foreign Intelligence Surveillance Court that there was reason to believe that Mr. Page may have been acting as a foreign agent on behalf of the Russians.
“The Republicans have chosen to wrap their arms around Page, and they may come to regret that,” said Jeffrey Smith, a former general counsel for the Central Intelligence Agency.
The memo actually undercuts the argument that a dubious warrant involving Mr. Page was the beginning of the Russia investigation, as it points out that the investigation began in July 2016 because of information about contacts between Russian intermediaries and another Trump campaign adviser, George Papadopoulos.
The New York Times reported in December that the inquiry was launched after Mr. Papadopoulos, during a night of heavy drinking, had told Australia’s top diplomat in Britain about these contacts, and the diplomat passed the information to the F.B.I.
How long the campaign by Mr. Trump and his associates against the F.B.I. lasts will most likely determine what, if any, long-term damage is done to the bureau. Mr. Smith, the former C.I.A. official, believes that the potential for harm is extensive, not least because foreign intelligence partners might be more reluctant to share information with the bureau.
But, he said, there could be significantly more harm if people begin looking for political motives in every action the F.B.I. takes.
“People across the country are going to say, ‘Can I trust the F.B.I.?’” he said.
