WASHINGTON (CN) - As he testified on his nomination to become homeland security secretary Wednesday, Oklahoma Senator Markwayne Mullin raised eyebrows among Senate lawmakers with claims that he went on a "classified," four-person trip to an undisclosed location a decade ago which required him to undergo military survival training.

The revelations prompted members of the Senate Homeland Security and Government Affairs Committee to demand a secure briefing with the nominee to discuss the details of the trip.

Mullin, tapped by President Donald Trump to replace Kristi Noem as head of DHS, was expected to face questions during his nomination hearing about reports that he has alluded in private to serving in war zones and doing security work for the U.S. government.

Asked Wednesday about the suggestion that he'd worked for the government abroad, the Oklahoma senator told members of the committee that there had been a "misunderstanding." Mullin said that he'd been asked in 2015 to train with a "very small contingency and go to a certain area" as part of his official duties as a member of the House, where he served from 2013 to 2023.

Mullin told lawmakers that he was asked to "meet certain training qualifications," and that he underwent Survival, Evasion, Resistance and Escape, or SERE, training - a specialized survival course for hostile environments developed by British special forces and adopted by the U.S. military.

"SERE training was absolutely awful, and I have spoken generally about my experiences, but I've never spoken specifically on details, on dates or on the mission," said the Oklahoma senator.

Mullin also pointed out that he had not mentioned the supposedly classified trip, which took place in 2016, in committee paperwork because it was an "official" trip he'd made as a member of Congress, which he said he was not required to report.

The DHS nominee's anecdote about a classified House excursion, which apparently came as a surprise to some members of the homeland security committee, prompted a flurry of questions from lawmakers trying to understand the scope of his travel.

But Mullin was largely evasive, repeating that the trip was "official" but also classified.

"I have zero issue talking about it, but I don't have the clearance to talk about it," he told members of the committee. He would not tell lawmakers who assigned him to the trip or who had classified it.

"Today is the first time I'm hearing about your classified activities from 2015 to 2016," said Michigan Senator Gary Peters, the top Democrat on the panel. "Quite frankly, as we've had these conversations, you've not been forthcoming."

Peters noted that the FBI had reviewed information from the State Department, the Pentagon and other intelligence agencies for classified documents mentioning Mullin.

"They said nothing showed up," the senator said. "You're in no classified document that the federal government has, according to the FBI, and yet you're telling me you did all this classified work."

Both Peters and committee chairman Senator Rand Paul asked Mullin if he would agree to brief lawmakers on the trip in the Senate's Sensitive Compartmented Information Facility. The DHS nominee was initially resistant but later agreed, if he could discuss the travel "in a classified setting."

Mullin agreed with members of the committee that anyone in the SCIF would need a Top Secret/Sensitive Compartmented Information security clearance, one of the highest U.S. government clearances.

As they left the SCIF in the bowels of the Capitol Wednesday afternoon, senators who attended the classified briefing had little they were willing to say about what they heard from Mullin. But some lawmakers' comments appeared to contradict the supposedly clandestine status of the nominee's past travel.

Connecticut Senator Richard Blumenthal told reporters that Mullin failed to answer "serious questions" about his supposed classified trip during the briefing.

"Some of his answers raise additional questions, and all of them go to his credibility," the senator said.

Blumenthal added that he had "really serious doubts" about whether Mullin had been fully forthcoming in his testimony and that he thought Paul should consider waiting to vote to advance the nominee out of the homeland security committee while lawmakers seek clarity.

"This whole situation strikes me as weird," said the Connecticut Democrat. "My personal impression is there is no need for this exchange to be classified - and why it was classified, and frankly who classified it, is still a mystery."

Pennsylvania Senator John Fetterman, who appeared open Wednesday to supporting Mullin's nomination, said he thought his colleagues were "preoccupied with a certain facet" of the Oklahoma senator's testimony, but did not offer his own view.

"There was a specific issue ... it wasn't my concern, but my colleagues had that," he said.

And Mullin's fellow Oklahoma Senator James Lankford told reporters the nominee's supposedly classified trip was related to a whistleblower and argued that the issue was little more than Democrats trying to dig up fresh dirt on Mullin ahead of his DHS confirmation vote.

"He came in and got it laid out," Lankford said. "Here's everything I can say and still honor non-disclosure on things. He gave a lot more detail than what he was able to do upstairs."

"People are going to find whatever they want to find," he added. "You're going to print whatever you want to print. I'm saying that if you know the whole story on it, this a mountain-molehill situation."

Notably, Lankford referred to a "non-disclosure" when talking about the nature of Mullin's resistance to speak publicly about the 2016 trip. Asked about the difference between "non-disclosure" and "classified," he said there were different terms "all being thrown around."

"I would use more the term of non-disclosure than classified, but I get those are two different things," he said. "I think even Markwayne wasn't careful in trying to be able to articulate between the two."

Mullin, for his part, declined to comment as he left the SCIF Wednesday afternoon. A spokesperson for his office did not immediately return a request for comment on whether he was under a non-disclosure agreement related to his 2016 trip or if it was indeed classified.

However, former House Speaker Kevin McCarthy, who attended Mullin's hearing in the homeland security committee, told reporters that his claims he was approved for a classified official trip in 2016 were "100% true," adding that he'd checked with the House speaker at the time, former Wisconsin Representative Paul Ryan.

For now, the uncertainty surrounding Mullin's supposedly classified excursion doesn't seem to have affected the timetable for his nomination to lead DHS.

The homeland security committee is expected to vote to advance him to a final confirmation vote Thursday morning, though Paul has said that could be subject to change. The committee chairman, who excoriated Mullin during Wednesday's hearing, has also said he will oppose the nominee.

If confirmed, Mullin will replace Noem at the Homeland Security Department once she leaves March 31.

Source: Courthouse News Service