WASHINGTON — The one-week clock on the F.B.I.’s new background investigation of Judge Brett M. Kavanaugh began ticking Saturday as Washington braced for the possibility of days of renewed political combat over whether he should be seated on the Supreme Court.
Law enforcement officials began reaching out to potential witnesses as they look into allegations of sexual misconduct by Judge Kavanaugh. Last week, Christine Blasey Ford, a research psychologist from California, described what she called a rape attempt by the judge in the early 1980s as she gave searing testimony before the Senate Judiciary Committee.
A lawyer for another accuser, Deborah Ramirez, a Yale classmate of Judge Kavanaugh’s who asserted that the judge exposed his genitals to her during a dorm party, said on Saturday that the F.B.I. had contacted him about talking with Ms. Ramirez.
“We can confirm the F.B.I. has reached out to interview Ms. Ramirez and she has agreed to cooperate with their investigation,” John Clune, her lawyer, said in a statement Saturday, declining to comment further.
Judge Kavanaugh angrily denied the accusations from both Dr. Blasey and Ms. Ramirez during his own testimony before the Judiciary Committee on Thursday.
At least one of the potential witnesses who is likely to be interviewed by the F.B.I. — Leland Keyser, who Dr. Blasey said was at the high school gathering where the assault is said to have occurred — notified the Judiciary Committee on Saturday morning that she would cooperate with the F.B.I.’s investigation.
Ms. Keyser, a longtime friend of Dr. Blasey’s, has said she does not recall the gathering in question. But her lawyer, Howard J. Walsh III, said in a letter to the committee that his client’s lack of a memory of the gathering does not mean she does not believe Dr. Blasey.
“Notably, Ms. Keyser does not refute Dr. Ford’s account, and she has already told the press that she believes Dr. Ford’s account,” her lawyer wrote. Dr. Blasey sometimes goes by her married name, Ford.
In his testimony on Thursday, Judge Kavanaugh claimed that Ms. Keyser’s earlier statements had “refuted” Dr. Blasey’s accusations.
The delay in a full Senate vote on Judge Kavanaugh’s confirmation to accommodate the new examination was forced on Friday by the Republican senators Jeff Flake of Arizona, Susan Collins of Maine and Lisa Murkowski of Alaska. Without their votes to confirm the judge, President Trump and Republican leaders in the Senate had no choice but to request an F.B.I. inquiry — a move that Democrats had demanded for days.
Mr. Flake, who is retiring, described to The Atlantic on Friday night his last-minute decision to change his mind on moving ahead with a quick confirmation of Judge Kavanaugh. Mr. Flake said he was motivated to call for a delay as a way to preserve the institutions of the Senate and the Supreme Court.
“The Supreme Court is the lone institution where most Americans still have some faith. And then the U.S. Senate as an institution — we’re coming apart at the seams,” Mr. Flake said, echoing remarks he made when he announced his retirement. “There’s no currency, no market for reaching across the aisle. It just makes it so difficult.”
Mr. Flake conceded that opponents of Judge Kavanaugh’s confirmation may try to use the delay to dig up more dirt on him. But the senator said that unless the F.B.I. investigation revealed new concerns, he was likely to support the judge’s confirmation.
“I’m a conservative. He’s a conservative. I plan to support him unless they turn up something — and they might,” said Mr. Flake, who has indicated that he would like the F.B.I. to speak to Mark Judge, a friend of Judge Kavanaugh’s whom Dr. Blasey has identified as a key witness to her allegation and who has disputed her account.
Still, the move left both parties nervous and uncertain about what might happen in the battle over the Supreme Court, which is playing out just weeks before voters go to the polls in elections that will determine control of Congress for the remainder of Mr. Trump’s term in office.
The nationally televised testimony by Dr. Blasey and Judge Kavanaugh may have deepened the divides in an already polarized electorate. If Judge Kavanaugh is confirmed, that could increase the number of women and liberals who turn out to vote. If he is rejected, enraged conservatives might surge to the polls.
The new investigation by the F.B.I. is a limited background check of Judge Kavanaugh, not a full-fledged criminal inquiry. The bureau is looking into only what it has been ordered to examine by the White House; the Judiciary Committee said the investigation should be limited to “current, credible allegations,” though it was unclear what those entailed.
It was also not clear whether the F.B.I. would investigate a series of allegations made by a third woman, Julie Swetnick, who has said that she witnessed a severely drunken Judge Kavanaugh mistreat women at parties in high school, and that he had been present at parties where high school boys gang-raped teenage girls.
“We have yet to hear from the FBI. When and if we do, we will promptly disclose to them all information and witnesses in our possession,” Michael Avenatti, a lawyer for Ms. Swetnick, said on Twitter on Saturday. “We continue to request this opportunity as we have been doing for days.”
Judge Kavanaugh has also forcefully denied the allegations by Ms. Swetnick, calling them completely false and ridiculous.
Senator Bernie Sanders, independent of Vermont, pressed on Saturday for an even broader investigation, writing in a letter to the chairman of the Judiciary Committee that the F.B.I. should examine whether Judge Kavanaugh lied to senators during his testimony.
“A fundamental question the F.B.I. can help answer is whether Judge Kavanaugh has been truthful with the committee. This goes to the very heart of whether he should be confirmed to the court,” Mr. Sanders wrote in the letter to the chairman, Senator Charles E. Grassley, Republican of Iowa. Some opponents of Judge Kavanaugh have questioned statements he made about his youthful drinking and his high school yearbook.
Mr. Sanders is unlikely to get his wish. In a statement Friday announcing that he had requested the F.B.I. inquiry, Mr. Trump said that it must be “limited in scope and completed in less than one week.”
It is clear, however, that Dr. Blasey’s accusations will be part of the new background investigation as agents try to determine who is telling the truth about what — if anything — happened between her and Judge Kavanaugh.
During his testimony, Judge Kavanaugh repeatedly said that Ms. Keyser, and two other people, had disputed Dr. Blasey’s allegations. Dr. Blasey had said that two of them were in the house, and that one of them — Mr. Judge, who said on Friday that he would cooperate with the F.B.I. investigation — was in the room at the time of the alleged assault.
“Dr. Ford’s allegation is not merely uncorroborated, it is refuted by the very people she says were there, including by a longtime friend of hers,” Judge Kavanaugh said on Thursday.
During the hearing, Dr. Blasey said she did not expect that Ms. Keyser would remember the gathering because Ms. Keyser was in another part of the house when the assault is said to have taken place. She told the senators that it was “a very unremarkable party” for Ms. Keyser. She also said that Ms. Keyser “has significant health challenges.”
“She let me know that she needed her lawyer to take care of this for her, and she texted me right afterward with an apology and good wishes,” she said.