Nearly three years after Justice Brett M. Kavanaugh’s tumultuous confirmation to the Supreme Court, the F.B.I. has disclosed more details about its efforts to review the justice’s background, leading a group of Senate Democrats to question the thoroughness of the vetting and conclude that it was shaped largely by the Trump White House.
In a letter dated June 30 to two Democratic senators, Sheldon Whitehouse of Rhode Island and Chris Coons of Delaware, an F.B.I. assistant director, Jill C. Tyson, said that the most “relevant” of the 4,500 tips the agency received during an investigation into Mr. Kavanaugh’s past were referred to White House lawyers in the Trump administration, whose handling of them remains unclear.
The letter left uncertain whether the F.B.I. itself followed up on the most compelling leads. The agency was conducting a background check rather than a criminal investigation, meaning that “the authorities, policies, and procedures used to investigate criminal matters did not apply,” the letter said.
Ms. Tyson’s letter was a response to a 2019 letter from Mr. Whitehouse and Mr. Coons to the F.B.I. director, Christopher A. Wray, posing questions about how the F.B.I.’s review of Mr. Kavanaugh was handled.
In an interview, Mr. Whitehouse said the F.B.I.’s response showed that the F.B.I.’s handling of the accusations into misconduct by Mr. Kavanaugh was a sham. Ms. Tyson’s letter, Mr. Whitehouse said, suggested that the F.B.I. ran a “fake tip line that never got properly reviewed, that was presumably not even conducted in good faith.”
Mr. Whitehouse and six of his Democratic colleagues on the Senate Judiciary Committee replied to the F.B.I.’s letter on Wednesday with demands for additional details on the agreement with the White House that governed the inquiry. They also pressed for more information on how incoming tips were handled.
“Your letter confirms that the F.B.I.’s tip line was a departure from past practice and that the F.B.I. was politically constrained by the Trump White House,” the senators wrote. Among those signing the letter were Senator Dick Durbin of Illinois, the committee’s chairman, Mr. Coons and Senator Cory Booker of New Jersey.
The F.B.I. declined to comment. Donald F. McGahn II, the White House’s general counsel at the time, did not respond to requests for comment.
Former President Donald J. Trump has long taken credit for Mr. Kavanaugh’s confirmation, which was almost derailed over allegations by a California professor that Mr. Kavanaugh had sexually assaulted her during a high school gathering in the early 1980s.
Despite widespread concern over the claims — which were followed by other allegations of sexual misconduct, all of which Mr. Kavanaugh has consistently denied — Mr. Trump steadfastly backed the judge. He deployed Mr. McGahn to shepherd Mr. Kavanaugh through the unusually fraught confirmation, which culminated in a heated, daylong hearing in September of 2018.
Both Christine Blasey Ford, the professor who said she was assaulted, and Mr. Kavanaugh were grilled by Senators on the Judiciary Committee.
In a recent interview with the author Michael Wolff, Mr. Trump put his handling of Justice Kavanaugh into stark terms, asking “Where would he be without me? I saved his life.”
But in addition to offering shows of support, the Trump White House carefully controlled the investigations into Mr. Kavanaugh’s past. After Dr. Ford came forward, Mr. Trump’s staff tried to limit the number of people the F.B.I. interviewed as part of that probe. Only after an outcry from Democrats over the president’s approach did the administration say the agency could conduct a more open investigation.
Ultimately, 10 witnesses were interviewed by the F.B.I., according to the F.B.I.’s recent letter. Dr. Ford and Mr. Kavanaugh themselves were never interviewed by the F.B.I.
Senator Richard Blumenthal, Democrat of Connecticut, who signed Wednesday’s letter to the F.B.I., called the process “an injustice in fact orchestrated by the White House under Donald Trump, an injustice that frankly was a disservice to the F.B.I.”
Debra Katz and Lisa Banks, the lawyers who represented Dr. Ford, said in a statement that the nation “deserved better” when it came to the inquiry into Justice Kavanaugh.