The Senate barreled on Friday toward a late-night vote on whether to confirm Pete Hegseth as secretary of defense, with the outcome still uncertain as a handful of Republicans weighed whether to back President Trump’s pick to lead the Pentagon.

Mr. Hegseth’s confirmation was further complicated earlier this week, when a former sister-in-law submitted a sworn statement to the Armed Services Committee accusing him of having been “abusive” toward his second wife and frequently intoxicated in public and private, including at least once while in uniform.

Mr. Hegseth denied the allegations in the affidavit, as he had denied an earlier allegation of sexual assault, as well as accusations of financial mismanagement and public intoxication. But the document has forced undecided Republicans to grapple anew with whether Mr. Hegseth has the character and comportment to manage an active-duty military of about 1.3 million service members and a Pentagon budget of nearly $850 billion.

Two Republican senators — Susan Collins of Maine and Lisa Murkowski of Alaska — have already publicly announced they intend to oppose Mr. Hegseth’s confirmation. If one more Republican were to join them, Vice President JD Vance could cast a tiebreaking vote to ensure his approval. But if more broke ranks, it would sink Mr. Hegseth’s bid.

In comments to reporters at the White House on Friday, Mr. Trump suggested he was bracing for at least one more Republican to potentially oppose Mr. Hegseth’s confirmation.

“I was very surprised that Collins and Murkowski would do that,” he said on the South Lawn as he departed for a trip to North Carolina and California. “And of course Mitch is always a ‘no’ vote I guess.”