WASHINGTON — The Senate, deeply divided over the results of an F.B.I. investigation into sexual misconduct allegations against Judge Brett M. Kavanaugh, moved uneasily toward a Friday morning vote that will most likely determine whether President Trump’s nominee will reach the Supreme Court.
Republican leaders were increasingly confident that despite a barrage of accusations, the Senate will narrowly vote to cut off debate on Judge Kavanaugh’s nomination and move to a final confirmation as early as Saturday. Because Republicans changed Senate rules last year to end filibusters for Supreme Court nominees, Friday’s vote will need the same 50 senators that the final confirmation tally will need.
But with four senators still undecided — the Democrat Joe Manchin III of West Virginia and the Republicans Jeff Flake of Arizona, Susan Collins of Maine and Lisa Murkowski of Alaska — Judge Kavanaugh’s confirmation was still not assured.
Judge Kavanaugh himself, in an extraordinary opinion article in The Wall Street Journal, tried to reassure those undecided senators that he possessed a proper judicial temperament after his emotional defense in a highly charged public hearing last week. He attributed his delivery to his “overwhelming frustration at being wrongly accused.”
“I was very emotional last Thursday, more so than I have ever been,” Judge Kavanaugh wrote in a piece that he conceived of himself. “I might have been too emotional at times. I know that my tone was sharp, and I said a few things I should not have said. I hope everyone can understand that I was there as a son, husband and dad.”
Republicans said the F.B.I. had turned up no evidence to corroborate accusations of sexual assault and misconduct, and their chances were bolstered when two undecided Republicans — Mr. Flake and Ms. Collins — signaled on Thursday that they were satisfied with the F.B.I.’s investigation.
“It appears to be a very thorough investigation,” Ms. Collins said Thursday morning before spending hours with the documents.
But there were also reasons for caution. One of two Democrats who were undecided on Thursday morning, Senator Heidi Heitkamp of North Dakota, announced that she could not vote for Judge Kavanaugh, shrinking the pool of potential yes votes in a Senate divided 51 to 49 in favor of Republicans. Ms. Heitkamp, who faces a difficult re-election race, invoked the testimony of Christine Blasey Ford, who said Judge Kavanaugh sexually assaulted her when she was 15.
“When I listened to Dr. Ford testify, I heard the voices of women I have known throughout my life who have similar stories of sexual assault and abuse,” Ms. Heitkamp said.
Mr. Flake, who said he had “seen no additional corroborating information” in the F.B.I. files, was nonetheless engaged in conversations with a Democratic colleague who helped force the F.B.I. investigation after last-minute negotiations last Friday.
“The materials are what they are, and it’s now left to senators to reach their conclusions,” the Democrat, Senator Chris Coons of Delaware, told reporters ruefully earlier in the day.
And in an unusual rebuke from a former member of the court, Justice John Paul Stevens, 98, said on Thursday that he had reluctantly concluded that Judge Kavanaugh was too prejudiced to effectively sit on the bench. He urged senators to carefully weigh the impact of his potential bias.
The senators made their views known during a tense and sometimes surreal day on Capitol Hill. Protesters massed near the Capitol and roamed the corridors of the Senate office buildings, pleading with Republican senators to vote no. Almost every undecided senator is receiving threats — at least one has been stalked at home — and many had police escorts.
Throughout the day, Republicans and Democrats streamed in and out of a secure underground room, where they took turns viewing the lone copy of the F.B.I. report. Swarms of reporters and photographers waited outside. In the ornate Senate chamber, members began giving dramatically divergent speeches about Judge Kavanaugh in anticipation of the Friday vote.
By day’s end, two competing narratives had emerged about the 46 pages of interview documents, nine of them devoted to a single witness: Mark Judge, a friend and high school drinking buddy of Judge Kavanaugh. One of the accusers, Dr. Blasey, says Mr. Judge was present when the future judge tried to rape her during a house party when they were in high school, most likely in the summer of 1982.
The F.B.I. also brought to the Capitol a towering stack of tips that the bureau had received but not followed up on.
While Republicans pressed on the idea that there was no corroborating evidence in the interviews, Democrats challenged the legitimacy of the investigation and the veracity of some of the witnesses. They said the F.B.I., at the White House’s direction, had left key witnesses off the interview list and left leads unexplored.
“What I can say is the most notable part of this report is what’s not in it,” Senator Dianne Feinstein of California, the top Democrat on the Judiciary Committee, told reporters at a brief appearance at the Capitol. Referring to the White House, she added, “It now appears that they also blocked the F.B.I. from doing its job.”
After viewing the documents, Senator Chuck Schumer of New York, the Democratic leader, said he was left with “serious doubts” about Judge Kavanaugh’s truthfulness about his past and rejected Republican assertions that Dr. Blasey’s story had been refuted by the interviews.
“To say that this investigation exonerates Judge Kavanaugh, or to say that this is a complete investigation, is patently false,” Mr. Schumer said.
But Republicans were determined to push forward. Most Republicans who left the secured briefing room said they were more confident supporting Judge Kavanaugh after the investigation.
“There’s nothing in it that we didn’t already know,” Senator Charles E. Grassley, Republican of Iowa and chairman of the Judiciary Committee, said in a statement Thursday. “These uncorroborated accusations have been unequivocally and repeatedly rejected by Judge Kavanaugh, and neither the Judiciary Committee nor the F.B.I. could locate any third parties who can attest to any of the allegations.”
Senator Mitch McConnell of Kentucky, the majority leader, accused Democrats of “partisan histrionics” and an “outrageous smear.”
“For goodness’ sake, this is the United States of America,” Mr. McConnell declared on the Senate floor. “Nobody is supposed to be guilty until proven innocent in this country. The Senate should not set a fundamentally un-American precedent here.”
In a nod to the raw politics unleashed in recent weeks, Mr. Grassley acknowledged the Senate had hit “rock bottom” and pledged to begin repairs. “I would like to have the future mending things, so we can do things in a collegial way,” he said.
The delivery of the report cleared the way for the Republican leadership to schedule a procedural vote on Friday, followed by a final confirmation on Saturday. But in a last-minute twist, a Republican senator — Steve Daines of Montana — said on Thursday night that he has a conflict: His daughter is getting married in Montana on Saturday.
With the Senate narrowly divided, Republicans need Mr. Daines’s vote. A spokeswoman for Mr. McConnell said his office was figuring out how to proceed.
Mr. Trump, for his part, alternated between cheering on Judge Kavanaugh and savaging Senate Democrats. “Due Process, Fairness and Common Sense are now on trial!” he wrote in one tweet.
Lawyers for Dr. Blasey, 51, and for Deborah Ramirez, 54, who says Judge Kavanaugh exposed himself to her at a party at Yale University, wrote to the F.B.I. on Thursday denouncing a “failure” to fully investigate their claims. Ms. Ramirez’s lawyer said his client had provided a list of more than 20 potential witnesses who he did not believe were interviewed. He also passed on multiple affidavits attesting to Ms. Ramirez’s claim.
“We can only conclude that the F.B.I. — or those controlling the investigation — did not want to learn the truth behind Ms. Ramirez’s allegation,” the lawyer, William Pittard, wrote.
Dr. Blasey’s lawyers provided the F.B.I. with the names of eight people they argued should have been interviewed, in addition to their client, and offered to provide additional evidence, including medical records. They said on Thursday that they got no response.
“The ‘investigation’ conducted over the past five days is a stain on the process, on the F.B.I. and on our American ideal of justice,” the lawyers wrote.
An official who reviewed the F.B.I.’s material said the bureau contacted 10 people and interviewed nine of them. The 10th person refused to be interviewed. Those interviewed included Ms. Ramirez and three people Dr. Blasey recalled being in the house at the time of the party: Mr. Judge, P.J. Smyth and Leland Keyser. All three have said they did not remember the party or witness misbehavior by Judge Kavanaugh, although Ms. Keyser told The Washington Post that she believes Dr. Blasey. Republicans briefed on their F.B.I. interviews said those witnesses did not change their accounts.
Also interviewed were two other high school friends of Judge Kavanaugh: Chris Garrett and Tim Gaudette.
But the four undecided senators will determine the fate of Judge Kavanaugh, 53, a 12-year veteran of the federal appeals court in Washington. Mr. Manchin said he would need to return on Friday before the vote to continue reviewing the F.B.I. summaries, but he said Ms. Heitkamp’s decision would not affect his.
The F.B.I. did not publicly explain why it stopped after talking with just nine people. The bureau apparently did not explore allegations by a third accuser, Julie Swetnick, who is represented by Michael Avenatti, a lawyer who also works for Stephanie Clifford, the former pornographic film actress known as Stormy Daniels who was paid hush money before the 2016 presidential election to keep her from discussing what she said was an extramarital affair with Mr. Trump.
The official who reviewed the material said the bureau focused on the episodes described by Dr. Blasey and Ms. Ramirez but did not go out of its way to pursue broader questions about Judge Kavanaugh’s drinking during high school and college.
The official said the bureau contacted one person who said he had heard about the episode involving Ms. Ramirez at Yale at the time, but that person did not witness it or talk with Ms. Ramirez. He identified the person he said had told him about the episode, but that person told the F.B.I. that he did not recall it, the official said.