Dozens of veterans -- some wearing service badges -- filled the hearing room in the Dirksen Building in support of Hegseth, wearing pins with the nominee's name. A number of them are wearing black baseball caps with the nominee's name and the bone frog logo associated with the Navy SEALs.

Spotted in the crowd were Sean Parnell, a former Army Ranger and conservative media personality, and Tim Kennedy, an ex-UFC fighter and former Green Beret.

The group, which was buzzing with excitement ahead of the hearing, appeared to cheer for Hegseth and shout "USA!" as the hearing got underway.

There are also a small group of Code Pink antiwar protestors in the room, with signs reading "No Hegseth No Crusade" and "No Hegseth No Christian Jihad."

-ABC News' Benjamin Siegel, Lauren Peller, Arthur Jones and Olivia Rubin

Sen. Jack Reed will tell Hegseth in no uncertain terms that he does not believe he is qualified for the job of Secretary of Defense.

"I do not believe that you are qualified to meet the overwhelming demands of this job," Reed will say, according to his opening statement.

Reed will also address the allegations against Hegseth, which Hegseth has denied.

"We must acknowledge the concerning public reports against you. A variety of sources -- including your own writings -- implicate you with disregarding laws of war, financial mismanagement, racist and sexist remarks about men and women in uniform, alcohol abuse, sexual assault, sexual harassment, and other troubling issues. I have reviewed many of these allegations, and find them extremely alarming," Reed will say.

He also alleges that Hegseth's comments suggest he will politicize the military.

"Indeed, the challenge of the Secretary of Defense is to remove partisan politics from the military. You propose to inject it. This would be an insult to the men and women who have sworn to uphold their own apolitical duty to the Constitution," the statement says.

-ABC News' Allison Pecorin

The FBI's probe of Hegseth did not include an interview with a woman who accused him of sexual assault years ago, sources familiar with the situation told ABC News.

Top senators on the Armed Services Committee were briefed on the FBI's background investigation last week but sources said investigators did not speak to the accuser. The circumstances around the lack of an interview with the woman are unclear.

A police report stated that a woman, identified only as Jane Doe, told investigators in 2017 she had encountered Hegseth at an event afterparty at a California hotel where both had been drinking and claimed that he sexually assaulted her. Hegseth had told authorities that the encounter was consensual.

No charges were filed, although Hegseth subsequently paid the woman as part of a settlement agreement, which Hegseth's attorney said was only because he feared his career would suffer if her allegations were made public.

Read more about the police report and alleged altercation here.

-ABC News' Rachel Scott, Katherine Faulders and Luke Barr

In a post on his social media platform, Trump wrote Hegseth will make a GREAT Secretary of Defense.

"He has my Complete and Total support. Good luck today, Pete!" Trump wrote.

Plus, Trump senior adviser Jason Miller did a morning show blitz praising Hegseth.

"I think Pete Hegseth is going to kill them with kindness," Miller said on CNN, previewing Hegseth's strategy ahead of the hearing.

On Fox News, Miller said he believed Hegseth was the war hero the United States needs and highlighted support from veterans for his nomination.

"I don't see it so much of a challenge. I think it's an opportunity to talk about restoring that warrior ethos, that warrior spirit, back into the military," Miller said as he avoided any concerns of Hegseth's past.

-ABC News Oren Oppenheim and Kelsey Walsh