That description was challenged by Chris Dudley, a former N.B.A. player and close friend of Judge Kavanaugh’s who attended Yale and played basketball with Mr. Ludington. Mr. Dudley said he was certain that he “never, ever saw Brett Kavanaugh black out” from drinking, and “never, ever saw him act inappropriately toward any woman in the 35 years that I’ve known him.”

The dueling statements emerged as the political combat around Judge Kavanaugh’s confirmation process intensified. Democrats lashed out over the size and shape of the inquiry, saying it threatened to become a sham that would deepen, rather than help heal, the country’s divisions about Judge Kavanaugh’s nomination.

Senator Mazie K. Hirono, a Hawaii Democrat on the Judiciary Committee, said on ABC’s “This Week” that any investigation that limits whom the F.B.I. can interview and which leads agents can follow would be a “farce.”

Senator Amy Klobuchar, a Minnesota Democrat who is also on the committee, described what she said was micromanaging from the White House: “You can’t interview this person, you can’t look at this time period, you can only look at these people from one side of the street from when they were growing up.”

“I mean, come on,” she said on CNN’s “State of the Union.”

Democrats were to some degree in the dark about the inquiry’s parameters. In a letter to Donald F. McGahn II, the White House counsel, and Christopher A. Wray, the F.B.I. director, the top Democrat on the Judiciary Committee asked for a copy of the directive sent by the White House to the bureau laying out the scope of the investigation.

“If the F.B.I. requests any expansion beyond the initial directive, please provide the names of any additional witnesses or evidence,” the Democrat, Senator Dianne Feinstein of California, wrote in the letter.

It is not unusual for the White House to specify the scope of a request for additional background information on a nominee. No evidence has emerged that the White House has forbidden any investigative steps, and President Trump has said he wants agents “to interview whoever they deem appropriate, at their discretion.”