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.
But the cautions Republicans received from the start about the materials did not stop them from repeating the unverified allegation hundreds of times over many months, in official settings and interviews on right-wing media outlets.
Representative James R. Comer, Republican of Kentucky and chairman of the Oversight Committee, called the source of the allegation “highly credible,” while Representative Jim Jordan, Republican of Ohio and the Judiciary Committee chairman, called the form the “most corroborating evidence we have.”
Representative Elise Stefanik of New York, the No. 3 House Republican who is one of Mr. Trump’s most vocal allies in that chamber, declared it “the biggest political corruption scandal, not only in my lifetime, but I would say the past 100 years.”
Republicans read it into the Congressional Record, included it as a “key” document on the House Republicans’ impeachment inquiry website and even threatened to hold the F.B.I. director, Christopher A. Wray, in contempt when he resisted their calls to send them an unredacted copy of the form.
Last week, a federal grand jury in California indicted the former F.B.I. informant who had made the accusation, Alexander Smirnov, on charges that he had fabricated the story in 2020 to help defeat Mr. Biden in the presidential campaign. Prosecutors also asserted in a court filing that Mr. Smirnov, a dual citizen of the United States and Israel who operated as a businessman and fixer in the former Soviet states, had told federal investigators that “officials associated with Russian intelligence were involved” in passing an unspecified story about Hunter Biden, the president’s son, who had been a board member of Burisma.
Current and former law enforcement officials said confidential informants dissemble all the time — often to impress their handlers or settle grudges — which is why the release of a raw, unverified report from a single source is strictly prohibited.
In a series of pointed letters to congressional Republicans last spring and summer, senior F.B.I. officials explained why they were unwilling to show the lawmakers the form containing the allegation, even in private.
“The mere existence of such a document would establish little beyond the fact that a confidential human source provided information and the F.B.I. recorded it,” wrote Christopher Dunham, acting assistant director of the agency, on May 10, 2023.
“Indeed, the F.B.I. regularly receives information from sources with significant potential biases, motivations and knowledge, including drug traffickers, members of organized crime, or even terrorists,” he added.
In another letter, Mr. Dunham warned Mr. Comer that revealing the unsubstantiated claims would endanger other confidential sources and have a “chilling effect” on recruiting others.
But a few weeks later, after House Republicans threatened to hold Mr. Wray in contempt of Congress for refusing to share the form, the bureau reluctantly agreed to provide a redacted copy for viewing at a secure facility on Capitol Hill. And several of the Republicans who saw it ignored the bureau’s warnings by describing its contents and citing it as proof positive that Mr. Biden was corrupt.
When news broke last week that the Justice Department had charged Mr. Smirnov with making it all up, Republicans downplayed their previous statements and blamed F.B.I. and Justice Department officials for telling them that the person who made the allegation was considered, in general, to be a credible source. (Both Democrats and Republicans agree bureau officials initially represented the source to Congress as “highly credible,” even if the allegations he passed along against Mr. Biden had not been verified.)
“I’m sure now they are apologizing,” Representative Ken Buck, a Colorado Republican who has been skeptical of the impeachment drive, said sarcastically of his colleagues. “I’m sure they’re saying, ‘Wow, Director Wray, you did the right thing. We really appreciate your professionalism.’”
Mr. Buck, a former prosecutor for 25 years, said the F.B.I. had handled the allegation the way every professional law enforcement agency should.
“You don’t go running to the press every time a witness says something, because you don’t know what the reliability of that testimony is,” Mr. Buck said. “It was premature to go out and tout how significant this was without knowing the reliability of the testimony.”
Despite the bureau’s warnings, and the inability of Republican investigators to produce evidence to support the bribery claims, members of the party’s right wing amplified their attacks, linking it to their impeachment inquiry.
Mr. Comer even chastised reporters for calling the allegations “unverified” instead of reporting that the informant was “highly credible” after lawmakers were shown the form.
In the following weeks, Mr. Comer, Mr. Jordan, Senator Josh Hawley of Missouri and many others touted the allegations.
Perhaps no one went quite as far as Ms. Stefanik, who went on Fox News to talk about what she characterized as the corruption scandal of the century.
“You have multiple members of the Biden family profiting illegally from foreign governments,” Ms. Stefanik said. “You also have the bombshell reporting, including potential tapes that exist, of while Joe Biden was vice president taking a bribe from Burisma.”
And Representative Anna Paulina Luna, Republican of Florida, said the document provided concrete evidence of what Republicans had suspected all along.
“This is absolutely something that Oversight has been speculating on,” she said. But now, she added, “we have proof.”
Weeks later, Representative Marjorie Taylor Greene of Georgia would read the allegations into the Congressional Record: “This form entails the damning information that then-Vice President Joe Biden took a $5 million bribe from the oligarch that owns Burisma. Not only did Joe Biden take a $5 million bribe, so did Hunter Biden.”
That, she added, was grounds enough to embark on the impeachment of Mr. Biden.
“What I am demanding is that the Republican-led House of Representatives move forward on an impeachment inquiry on Joe Biden, because this type of corruption should never be allowed to stand,” she said.
The indictment unsealed in California federal court portrays Mr. Smirnov as a serial liar whose motivation for targeting the Bidens appeared to have been rooted in the same political animus that drove Republicans to promote his claims.
During the 2020 campaign, he sent his F.B.I. handler “a series of messages expressing bias” against Mr. Biden, including texts, replete with typos and misspellings, boasting that he had information that would put him in jail.
In the wake of Mr. Smirnov’s indictment, Democrats have called for an end to the impeachment inquiry.
Representative Dan Goldman, a New York Democrat who was a federal prosecutor, said the F.B.I. should never have released the Form 1023.
“It is really a dereliction of duty as an investigator to do what they did, and that is also another reason why this investigation should be terminated immediately,” he said.
Rather than admitting they overhyped the evidence, Republicans have pivoted.
Despite his role in kicking off the frenzy, Mr. Grassley’s office denied the Iowan had promoted the allegations, saying that he “only ever asked what the F.B.I. did to investigate the allegations and verify them.”
Mr. Grassley’s spokeswoman also claimed a bit of victory, because, she said, the senator had forced the F.B.I. to finally investigate the claim. “Given the timeline provided in the D.O.J.’s indictment, it’s clear that the F.B.I. only began investigating after Senator Grassley made the 1023 public,” she said.
Mr. Comer now says the impeachment inquiry “is not reliant” on the form detailing the bribery allegation.
Mr. Jordan said Mr. Smirnov’s indictment “doesn’t change the fundamental facts” of the case against Mr. Biden.
Republicans quietly deleted a reference to the document from a request to interview a witness in their impeachment inquiry.
And by Friday, under the section of the impeachment inquiry website called “Key Evidence,” the 1023 form had been removed.
Kenneth P. Vogel contributed reporting. Zach Montague and Kitty Bennett contributed research.