In September 2018, as allegations of sexual misconduct against Brett M. Kavanaugh threatened his confirmation to the Supreme Court, President Trump vowed that the FBI would have “free rein” to vet the claims. Trump said the FBI was “talking to everybody” and added on social media: “I want them to interview whoever they deem appropriate, at their discretion.”

The president’s comments came as a surprise to the FBI, according to a new report from a Democratic senator based on previously undisclosed correspondence between the agency and the White House. FBI officials — directed to conduct a very limited inquiry in a week’s time — requested “additional guidance” from the White House, citing the public remarks by Trump and other officials describing a freewheeling investigation. But the White House never authorized the agency to independently probe the sexual misconduct allegations, which Kavanaugh staunchly denied.

The report, which was produced by Sen. Sheldon Whitehouse (D-R.I.), a Judiciary Committee member and leading critic of the Kavanaugh confirmation, and provided to The Washington Post ahead of a public release on Tuesday, provides additional evidence of the tight control exercised by the White House over the FBI investigation — despite Trump’s claims to the contrary.

The report found that messages to the FBI tip line regarding Kavanaugh were forwarded directly to the White House and never probed, and that the FBI had no written protocols for the supplemental background investigation ordered by the White House. It notes that the FBI was instructed by the White House to talk to 10 potential witnesses and was not given the leeway to pursue corroborating evidence — the absence of which was cited by senators as they narrowly voted to confirm Kavanaugh, marking a major triumph for the conservative movement and locking in a right-leaning majority that would later overturn the constitutional right to abortion.

Trump ordered the additional inquiry following nationally televised testimony by Christine Blasey Ford that Kavanaugh had groped her and tried to take off her clothes more than three decades earlier, when they were in high school at a party in suburban Maryland. Another accuser, Deborah Ramirez, had come forward in a New Yorker story, saying Kavanaugh had shoved his penis into her face during a dorm party when they were at Yale University in the early 1980s.

“The Congressional report published today confirms what we long suspected: the FBI supplemental investigation of then-nominee Brett M. Kavanaugh was, in fact, a sham effort directed by the Trump White House to silence brave victims and other witnesses who came forward and to hide the truth,” said Blasey Ford’s lawyers, Debra Katz and Lisa Banks.

An attorney for Ramirez, John Clune, said of the report: “It’s really disappointing since our client was so candid about something that was a pretty awful experience.”

Kavanaugh did not respond to a request for comment sent to the Supreme Court on Monday. Trump campaign spokeswoman Karoline Leavitt said Kavanaugh “was unfairly slandered and smeared with lies.”

Some of the limits placed by the Trump White House on the inquiry were widely reported at the time. The FBI did not question Kavanaugh or Blasey Ford about the allegations. Nor did the FBI interview dozens of people whose names were provided by lawyers for Blasey Ford and Ramirez who said they could have offered corroborating evidence. It was also clear at the time that the FBI was not conducting a criminal investigation in which it would have broad authority,

The FBI declined to comment on the report but explained in a statement how it responds to requests from the White House to conduct background investigations.

“The FBI follows a long-standing, established, process through which the scope of the investigation is limited to what is requested,” the statement said. “The FBI does not have the independent authority to expand the scope of a supplemental background investigation outside the requesting agency’s parameters.”

In an interview, Whitehouse said the review of the FBI probe took six years because of resistance from both the Trump and Biden administrations to providing correspondence with the FBI, access to FBI officials and answers to questions about the investigation. Until 2021, the only information Democratic senators said they were able to obtain about the procedures for a supplemental background investigation was a publicly accessible YouTube video explaining how the FBI tip line works.

“Assurances that everything was being done by the book and according to standard FBI procedures omitted the fact that for supplement background investigations, there is no book and there are no procedures,” Whitehouse said. “You simply do what the White House tells you.”

The report notes there was no dedicated tip line set up for the Kavanaugh inquiry; members of the public used a preexisting portal called the National Threat Operations Center. The FBI received more than 4,500 calls and electronic messages related to Kavanaugh and was directed to forward the tips to the White House without pursuing any possible leads, according to the report. Even when senators contacted the FBI directly with the names of people who claimed to have relevant information about Kavanaugh, the FBI did not contact them.

The report described how two days before voting on Kavanaugh, senators were given about an hour to review more than 1,600 pages of material collected by the FBI, mostly raw information from the tip line. Neither the FBI nor the White House explained whether the tips had been reviewed, Whitehouse said.

“It all went up to the White House for a decent burial,” Whitehouse said, “with no investigation whatsoever.”