In May 2023, Senator Charles E. Grassley, a chief antagonist of President Biden, strode to the Senate floor with some shocking news: He had learned, he said, of a document in the F.B.I.’s possession that could reveal “a criminal scheme involving then-Vice President Biden.”
Mr. Grassley, an Iowa Republican, suggested to any Americans listening that there was a single document that could confirm the most sensational corruption allegations against Mr. Biden — and that the Federal Bureau of Investigation was engaging in a coverup.
“Did they sweep it under the rug to protect the candidate Biden?” he asked conspiratorially.
Over the next few months, Mr. Grassley’s quest to make public the allegation — laid out in an obscure document known as an F.B.I. Form 1023 — became a fixation, and a foundation of the growing Republican push to impeach Mr. Biden as payback for Democrats’ treatment of former President Donald J. Trump.
At the center of it all was the unsubstantiated accusation that Mr. Biden had taken a $5 million bribe from the executive of a Ukrainian energy company, Burisma.
But what neither Mr. Grassley nor any of the other Republicans who amplified the claims said in their breathless statements was that F.B.I. officials had warned them repeatedly to be cautious about the accusation, because it was uncorroborated and its credibility unknown.
All that the form proved, federal law enforcement officials explained, was that a confidential source had said something, and they had written it down. And now federal prosecutors say the claim was made up.
