Sen. Lisa Murkowski, R-Alaska, announced she will vote against Pete Hegseth's nomination for secretary of defense.

Murkowski is the first Republican to publicly oppose Hegseth's nomination. Her opposition comes amid reports by NBC News and other sources that senators are raising questions about Hegseth's vetting process, pointing to allegations of abuse and drinking made by his former sister-in-law and saying President Donald Trump's transition team had not disclosed them.

Danielle Hegseth, the nominee's former sister-in-law, said in an affidavit that he had made his ex-wife, Samantha Hegseth, fear for her safety.

Samantha Hegseth denied that there was any "physical abuse" in their marriage. 

"Managing the Department of Defense requires vast experience and expertise as the department is one of the most complex and powerful organizations in the world, and Mr. Hegseth's prior roles in his career do not demonstrate to me that he is prepared for such immense responsibility," Murkowski posted on X. "His leadership of two veteran organizations was marked with accusations of financial mismanagement and problems with the workplace culture he fostered."

The Alaska senator also said she was concerned about the twice-divorced Hegseth's admission of infidelity and said character is the defining trait required of the secretary of defense.

"The past behaviors Mr. Hegseth has admitted to ... demonstrate a lack of judgment that is unbecoming of someone who would lead our armed forces," Murkowski wrote. "These behaviors starkly contrast the values and discipline expected of servicemembers. Men and women in uniform are held accountable for such actions, and they deserve leaders who uphold these same standards."

Murkowski also highlighted Hegseth's previous opposition to women in combat, though Hegseth now says he supports women in combat, provided they meet the same standards as men.

"Women have served our nation with distinction, overcoming immense obstacles to excel in combat and leadership roles, and they deserve to know that their leader honors and values their commitment to our nation," Murkowski said.

Hegseth can afford to lose only three Republican senators if Democrats vote in opposition to oppose. Sen. Joni Ernst, R-Iowa, said she will continue to support his nomination.

"The ex-wife has denied the allegations," she said. "I think we need to take her at her word."

• Armed Services Chair Wicker: Republicans Backing Hegseth
• Sen. Marshall to Newsmax: Hegseth Claim 'Very Timed' by Dems