In the midst of the 2016 presidential primary season, the FBI received a purported Russian intelligence document describing a tacit understanding between the campaign of Hillary Clinton and the Justice Department over the inquiry into whether she intentionally revealed classified information through her use of a private email server.

The Russian document mentioned a supposed email describing how then-Attorney General Loretta E. Lynch had privately assured someone in the Clinton campaign that the email investigation would not push too deeply into the matter — a conversation that if made public would cast doubt on the inquiry’s integrity.

Current and former officials have said that document played a significant role in the July decision by then-FBI Director James B. Comey to announce on his own, without Justice Department involvement, that the investigation was over. That public announcement — in which he criticized Clinton and made extensive comments about the evidence — set in motion a chain of other FBI moves that Democrats now say helped Trump win the presidential election.

But according to the FBI’s own assessment, the document was bad intelligence — and according to people familiar with its contents, possibly even a fake sent to confuse the bureau. The Americans mentioned in the Russian document insist they do not know each other, do not speak to each other and never had any conversations remotely like the ones described in the document. Investigators have long doubted its veracity, and by August the FBI had concluded it was unreliable.