"This information is quite disturbing, sir," he wrote to Major General William Walker, the commanding general of the Washington, D.C., National Guard, who was helping bolster security in the U.S. capital for Joe Biden's presidential inauguration on Jan. 20.

Hegseth, Gaither wrote, had a worrying tattoo on his bicep with the inscription "Deus Vult." A search online suggested to him it was Christian expression associated with right-wing extremism. "Deus Vult" is a Latin phrase meaning "God Wills It," a rallying cry for Christian crusaders in the Middle Ages.

Gaither included a photo of Hegseth, who was then and still is a Fox News host, shirtless, showing another tattoo of the Jerusalem Cross. That cross has a long history in Christianity but has lately been co-opted by some far-right groups as a symbol of the fight for Western civilization.

"This falls along the lines of an insider threat," wrote Gaither, who was the Guard's head of physical security but is now retired from military service. He read his email to Reuters.

The email, which has not been previously reported, appears to have been a turning point for Hegseth, who served in Afghanistan, Iraq and Guantanamo Bay, Cuba and has two Bronze Stars. In his book, Hegseth wrote that he was singled out over the Jerusalem Cross as an extremist, and pulled from Guard duty in Washington.

He saw it as a rejection by a military that didn't want him anymore.

"The feeling was mutual - I didn't want this Army anymore either," Hegseth said in his book "The War on Warriors: Behind the Betrayal of the Men Who Keep Us Free."

The National Guard has not commented on Hegseth's tattoos, his allegations of being targeted for his religious and political beliefs, or whether he was withdrawn from Guard duty in Washington. Trump's transition team did not immediately reply to a request for comment.

Reuters does not have a copy of the email and cannot independently corroborate Gaither's account.

But a second member of the D.C. National Guard at the time, who has since left the service, confirmed that Hegseth's tattoos were the reason he was flagged for review, and that there were email exchanges within the organization about them.

Hegseth was not declared an extremist, this person said, speaking on condition of anonymity. But in the wake of the Jan. 6 riots Guard leadership opted to err on the side of caution.

Asked about the tattoos, Heidi Beirich, co-founder of the Global Project Against Hate and Extremism, which works to combat far-right extremism, did not dismiss the concerns. But she cautioned against any quick judgment, saying they could be just signs of Hegseth's Christian faith even if they have been used by extremist groups.

"I think we have to take his word for it," Beirich told Reuters.

Trump's pick of Hegseth to become his defense secretary caught Washington by surprise. Hegseth, who appears frequently on conservative media, has expressed disdain for so-called "woke" policies of Pentagon leaders, opposed women in combat roles, and questioned whether the top American general, who is Black, was in his role because of his skin color.

If confirmed by the U.S. Senate, Hegseth could make good on Trump's campaign promises to rid the U.S. military of generals he accuses of pursuing progressive policies on diversity in the ranks that conservatives have railed against.

"STAND DOWN"

How Hegseth became an "anti-woke" advocate is still coming into view. But it is becoming increasingly clear that he came to a crossroads in January 2021.

In a podcast last month, Hegseth said he had military orders to go to Washington, D.C., for inauguration security but received a call from one of his commanders a day before he was to report to the D.C. National Guard.

"Major, you can stand down. We don't need you. We're good," Hegseth recounted being told. He said he was told his orders had been revoked.

Hegseth said he was not told at the time why he was no longer needed, but when he was writing his latest book he reached back out to the individual.

"He said: 99.99% I know why you were... told not to report, because I saw the emails and I was in the meetings, someone identified a Jerusalem cross tattoo you have on your chest... as an extremist tattoo and so you were dubbed as a possible extremist, white nationalist specifically."

"Was it because of the tattoo, probably not. Was it because I worked for Fox, I don't know. Was it because I support Donald Trump, I don't know. Any of those are unacceptable reasons," Hegseth wrote.

"That was the moment I said, I'm done."

Hegseth was not the only person removed from Guard duty on inauguration day four years ago. On Jan. 19 2021, a day before Biden's inauguration, Pentagon officials told reporters that a dozen members of the National Guard had been removed from duty after vetting, which included screening for potential ties to right-wing extremism.

A Pentagon spokesman said at the time that the vetting went beyond ties to extremist groups. One Guard member was removed from duty after troubling text messages and another had been reported to a tip line.

The officials did not name any of those individuals and it is not clear if Hegseth was included in those numbers.

Gaither, who was tipped off to Hegseth by a former member of the Guard, said he stands by his decision to flag him for the tattoos. His job was to ensure the safety of the force and he sent the information up his chain of command for a decision.

"I'm not backing down from it at all," Gaither said. "I did what I was supposed to do as a leader, and I sent it forward."