Live Updates: Hegseth Confirmation Uncertain as Senate Prepares to Vote

“We cannot risk installing a leader who may have a history that is exploitable by our adversaries,” Senator Jack Reed of Rhode Island, the top Democrat on the Armed Services Committee, said in a floor speech on Thursday. “Nor can we risk confirming a secretary of defense who has shown that he is incapable of being responsible, accountable and law abiding 24 hours a day, seven days a week, as that job requires.”

In his statement, Mr. Reed referred to a sworn statement submitted to the Senate on Tuesday by a former sister-in-law of Mr. Hegseth’s who described him as frequently intoxicated and “abusive” toward his second wife. Mr. Hegseth, 44, has denied the account, along with several other allegations that have dogged his nomination, including one of sexual assault, and other reports of excessive drinking.

A handful of Republicans had said privately that the new allegations from Danielle Diettrich Hegseth, the former wife of Mr. Hegseth’s brother, were concerning. But on Thursday, all but two, Senators Susan Collins of Maine and Lisa Murkowski of Alaska, voted to advance his nomination.

Before the vote, Ms. Murkowski said that she could not “in good conscience” support installing Mr. Hegseth at the Pentagon.

“While the allegations of sexual assault and excessive drinking do nothing to quiet my concerns, the past behaviors Mr. Hegseth has admitted to, including infidelity on multiple occasions, demonstrate a lack of judgment that is unbecoming of someone who would lead our armed forces,” she said in a statement, which also cited reports of alleged financial mismanagement at two veterans’ organizations he ran, as well as his past statements disparaging the role of women in combat.

After the vote, Ms. Collins said in a statement that she would oppose Mr. Hegseth’s confirmation when it came to a final vote on Friday, as she was “concerned that he does not have the experience and perspective necessary to succeed in the job.”

She did not mention the affidavit, the allegation that Mr. Hegseth committed sexual assault or reports that he was frequently intoxicated, in public and private — all of which he has denied. Instead, she cited his lack of management experience, his stated views disparaging the role of women in the military, and his expressed skepticism about prohibitions against torture and the Geneva Conventions, as reasons she opposed his bid.

To win confirmation, Mr. Hegseth can lose the support of no more than three Republicans given that Democrats are all but certain to oppose him unanimously, as they did on Thursday. Should more G.O.P. senators decide to join them in opposition on Friday, his Senate approval could come down to the wire, potentially requiring the intervention of Vice President JD Vance to break a tie and give him the necessary majority to be confirmed.

From the beginning, Mr. Trump’s selection of Mr. Hegseth, a former Fox News host and veteran of the wars in Iraq and Afghanistan, has generated controversy, so much so that the president considered dropping him amid resistance from senators in both parties. But Mr. Trump dug in behind him and Mr. Hegseth has aggressively made his case on Capitol Hill. During his confirmation hearing, he called the raft of allegations that had surfaced against him “anonymous smears.”

Samantha Hegseth, Mr. Hegseth’s second wife, has said publicly that he never physically abused her. But a Trump transition official informed the leaders of the Armed Services Committee last week that she had told the F.B.I. during a background interview that Mr. Hegseth abused and continues to abuse alcohol, according to a person with knowledge of the findings.

Senator Roger Wicker, Republican of Mississippi and the chairman of the committee, made no specific mention of the allegations in making the case for Mr. Hegseth on the Senate floor, but decried what he called the “numerous smears and false news stories” about him.

“His experience in the line of fire and his service member advocacy make at least one thing clear: Pete Hegseth will put the men and women of our military first,” Mr. Wicker said.

But Democrats warned that he was egregiously unqualified for the job Mr. Trump wants him to have.

“Is this man, with a known history of excessive drinking, the guy you want at the other end of the phone at 2 a.m. in a crisis, in control of the nuclear codes? Who are we kidding?” said Senator Chuck Schumer, Democrat of New York and the minority leader, adding: “Pete Hegseth has proven to lack the necessary morality, sense, judgment” to be secretary of defense.

Danielle Hegseth’s affidavit, obtained by The New York Times, described Mr. Hegseth as demonstrating such “erratic and aggressive behavior” that his second wife, Samantha Hegseth, once hid in a closet from him, and gave close friends a safe word so that she could call for help if she needed it. It also details several episodes in which she said she personally witnessed Mr. Hegseth drink to excess, including once while in uniform and several times to the point of passing out.

Democrats were racing on Thursday to bolster those allegations with further testimony or evidence, according to people familiar with their efforts.

But many Republicans had already dismissed the allegations, pointing to Samantha Hegseth’s denial.

“Why should I trust her word?” Senator Lindsey Graham, Republican of South Carolina, said of Danielle Hegseth in a brief interview on Wednesday. “He said no. Seems like there’d be other people out there if he was stumbling down falling drunk all the time.”

Senator Joni Ernst, Republican of Iowa and an early skeptic of Mr. Hegseth’s nomination who moved to staunchly back him, was similarly unmoved.

“His ex-wife has denied it. So it really doesn’t go very far,” Ms. Ernst, who came under immense pressure from Mr. Trump’s supporters to support Mr. Hegseth, told reporters at the Capitol on Wednesday. “It carries no weight.”

A handful of Republican senators were noncommittal, giving Democrats hope that they might yet be able to persuade enough others to block Mr. Hegseth’s bid.

Senator Thom Tillis, Republican of North Carolina, told reporters on Thursday he was continuing to do his “due diligence” on the nomination, even as he voted to break the Democratic filibuster.

Senator Mitch McConnell, Republican of Kentucky, who has not endorsed Mr. Hegseth, has refused to answer questions about his bid, but voted Thursday to advance Mr. Hegseth’s nomination toward a final confirmation vote.