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The now-discharged Marine who was previously confined to a North Carolina brig after speaking out in the United States' disastrous withdrawal from Afghanistan told Fox Nation on Wednesday that Biden defense secretary Lloyd Austin shocked him by claiming COVID-19 is the greatest threat to the Pentagon.

Lt. Col. Stuart Scheller Jr. told "Tucker Carlson Today" that previous remarks from Austin made him "want to put my head through a wall" – after the defense secretary claimed in a 2021 memo that the "greatest proximate challenge to our nation's security is the threat of COVID-19."

In the memo, Austin promised to "continue to act boldly and quickly to support Federal Government efforts to defeat the disease, defend the force against it, and work with our domestic and international partners to protect our Nation from potential novel and deadly viruses of the future."

In a video, Marine Lt. Col. Stuart Scheller demanded senior U.S. leaders hold themselves accountable for actions made during the U.S. military's withdrawal from Afghanistan that led to the deaths of 13 service members.

In a video, Marine Lt. Col. Stuart Scheller demanded senior U.S. leaders hold themselves accountable for actions made during the U.S. military's withdrawal from Afghanistan that led to the deaths of 13 service members.  (Scheller video screenshot)

"[T]hese challenges demand of us an aggressive effort to inform and educate people about the safety and efficacy of available vaccines and protective measures," the former CENTCOM commander wrote.

Scheller recounted how Austin came to be Biden's Pentagon chief from a lucrative private sector post on the board of Massachusetts-based defense contractor Raytheon Technologies.

"So then he comes off the Raytheon board, becomes the secretary of defense – arguably the best job in the world," he said. "He spends 100 days as secretary defense-- comes out and is like, 'I've orientated on the problem and the biggest problem facing the DOD is COVID.'"

Secretary of Defense Lloyd Austin III pauses while speaking during a media briefing at the Pentagon, Wednesday, Nov. 17, 2021, in Washington.

Secretary of Defense Lloyd Austin III pauses while speaking during a media briefing at the Pentagon, Wednesday, Nov. 17, 2021, in Washington.  (AP Photo/Alex Brandon)

"I was ready to put my head through a wall – it was like, ‘Are you kidding? The biggest threat is COVID?’ There are things rotting us from the bottom. Either you just don't know or you are playing a political game, but it doesn't matter because you are not benefiting the junior service member if that is your diagnosis of the problem."

Scheller said the military has many fundamental problems, including in the fields of procurement and education, and that coronavirus is nowhere near the top of that list.

In recent months, the Biden administration has handed down several vaccine mandates, including via the Pentagon. However, a Bush-appointed Texas judge recently issued a temporary injunction in favor of a group of Marines potentially facing discharge amid rejected religious exemptions to the Pfizer, Johnson & Johnson, or Moderna-produced injections.

Trouble for Scheller started after he posted videos on social media in August criticizing the Afghan exit. He pleaded guilty to six misdemeanor-level violations of military law on Oct. 15 during a special court-martial after spending nine days in the brig at the Marine Corps' Camp Lejeune in Jacksonville, N.C.

Military Judge Col. Glen Hines sentenced him to a letter of reprimand and a $5,000 fine – far less than prosecutors' recommendation of a $30,000 fine. The judge noted Scheller’s flawless 17-year record prior to the posting the videos and said he "appeared to be someone in pain."

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In a lengthy Facebook post, Scheller recapped what he went through. As he returns to civilian life he remains thankful for what his military experience provided.

"I was released from the Marine Corps today, Thursday, December 23rd, 2021. I am filled with mixed emotions. I would like to sincerely thank the Marine Corps for forging me into a man," Scheller said. "And from the bottom of my heart, I’d like to thank all the Marines who served, led, bled, and suffered alongside me the past 17 years.

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Austin is not the first brass to be criticized for his comments about threats to the military.

Joint Chiefs Chairman Gen. Mark A. Milley came under fire for testimony about "White rage" being a national crisis, amid public objections over the Pentagon's sudden focus on"‘wokeness" in some regards early in 2021.

At the time, host Tucker Carlson called Milley "dishonest, incompetent, partisan, and dishonorable."