In those final days, F.B.I. leaders appeared to be caught in a whirlwind of anti-Clinton rumors and speculation. In his report, Mr. Horowitz acknowledges the role that the threat of leaks played in the F.B.I. leadership’s decision to make the news about Mr. Weiner’s laptop public. Numerous agents and officials confirmed it: Mr. Strzok and Lisa Page , an F.B.I. lawyer at the time; James Rybicki, then the F.B.I. chief of staff ; James Baker, then the F.B.I. general counsel; and Sally Yates, then deputy attorney general.

“The discussion was somebody in New York will leak this,” Mr. Baker said. “If we don’t put something out, somebody will leak it.”

“Numerous witnesses connected this concern about leaks specifically” to the New York office and “told us that F.B.I. leadership suspected that F.B.I. personnel” in that office were “responsible for leaks of information in other matters,” the inspector general’s report said. “Even accepting Comey’s assertion that leaks played no role in his decision, we found that, at a minimum, a fear of leaks influenced the thinking of those who were advising him.”

Ms. Yates told investigators that the F.B.I. explicitly cited the threat of leaks in explaining its decision to go public to the Justice Department. As she recalled, one reason the F.B.I. officials gave for why they felt Mr. Comey had to go to Congress “is that they felt confident that the New York field office would leak it and that it would come out regardless of whether he advised Congress or not.”

The F.B.I. agent corps today overwhelmingly fits the demographic profile of a Trump voter. During the 2016 campaign, in The Guardian, one agent said, “The F.B.I. is Trumpland.” In his testimony, Mr. Strzok all but laughed out loud when committee members pressed him Thursday on whether the whole F.B.I. was made up of Democrats.

The New York field office, one of only three headed not by a special-agent-in-charge but by a full assistant director, has always been a particular challenge for bureau leaders — it’s fiercely independent, combative and notoriously leaky. The office, which works closely with the local United States attorney for the Southern District of New York, a job held by both Mr. Comey and Mr. Giuliani, is sometimes referred to inside the Justice Department as the “Sovereign District of New York” for charting its own course.

The office has long been a source of meddlesome leaks, in part because of the intermixing of F.B.I. agents and New York Police Department officers who have close relationships with the city’s press corps. The lowest point in these relations came in 2009, when the investigation of the would-be subway bomber Najibullah Zazi — a critical emergency investigation that had remained secret when it was focused in Denver, Zazi’s hometown — leaked quickly once the would-be attacker and case arrived in New York, both to the media and to the suspect’s family itself.