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In a rare assurance to young immigrants serving in the military who were brought to the US illegally by their parents, Defense Secretary James Mattis on Thursday said they would continue to be protected from deportation even if their current legal protections expire next month.

“We would always stand by one of our people,” Mattis told reporters at the Pentagon. “Our guys on active duty, and that sort of thing … are not in any kind of jeopardy.”

The Pentagon chief said he confirmed that position in a phone call earlier on Thursday with Homeland Security Secretary Kirstjen Nielsen. He said the two had gone over the issue “in great detail.”

The Deferred Action for Childhood Arrivals program, or DACA, is set to expire on March 5. However, even if Congress fails to act before the deadline, DACA recipients in the military will still “not be subject to any kind of deportation,” Mattis said.

There are roughly 900 DACA recipients serving in the military, according to the Pentagon. Only DACA recipients with highly sought language and medical skills are allowed to enlist, through a program that offers a fast track to citizenship in exchange for their service. More than 10,400 immigrant recruits have earned their citizenship through the Military Accessions Vital to National Interest program, or MAVNI, since 2009. That includes many DACA recipients who've been eligible to enlist since 2014.

Several DACA recipients enlisted in the military told BuzzFeed News they were skeptical of Mattis's vow to protect them.

“It's really nice of him to say that, but I don't think his words really hold any weight because I doubt ICE will listen to what he says,” said Harminder Saini, a 24-year-old US Army recruit who is a DACA recipient.

If Mattis really wants to protect DACA recipients, Saini said, he should reactivate the flailing MAVNI program, which has been plagued by long delays that place hundreds of immigrant soldiers in legal limbo while postponing the citizenship they were promised. The program is supposed to allow those in it to apply for citizenship immediately after entering basic training, but recent changes have delayed that process.

“Citizenship for us is what ultimately will protect us,” Harminder said.

Others told BuzzFeed News that they were encouraged by Mattis's pledge, and hoped it meant they could enter military service sooner rather than later.

“I honestly trust Secretary Mattis more than Congress, the Army, or (anyone else) in the Trump administration,” said William Medeiros, a 25-year-old US Army recruit who was born in Brazil and brought to the US as a child. Like many MAVNI military recruits, his background checks have been stalled for months. Medeiros, for example, said he's been waiting 18 months to be told to report to basic training.

“Citizenship is important, yes, but I’d rather be at basic training more than anything and start the process already,” he told BuzzFeed News. “We’ve been waiting for years. The delayed bureaucratic promises from the Army are playing with our lives.”

On Thursday, Mattis said any DACA recipient serving active duty, as well as those in the active reserves, those with an honorable discharge, and those who enlisted in the military and are waiting to go to basic training, should not fear deportation even if their status expires. The only exceptions would be anyone charged with a serious felony or subject to a final deportation order, he said, adding that he knew of no cases for the latter.

His comments came after Pentagon officials earlier on Thursday declined to say what steps the Defense Department was taking to protect DREAMers serving in the military.

“Ultimately, this is a legislative decision,” Pentagon spokesperson Dana White said at a news briefing, adding that the military was working with the Justice and Homeland Security departments. “We'll continue to work to ensure that we … comply with the law.”

Mattis’s assurances present a stark contrast to the rest of the Trump administration, which in September announced that it would end the program that protects 700,000 immigrants who came to the US without proper documentation as children and has been loath to give any guarantees.

On Wednesday, White House chief of staff John Kelly, who previously led the Homeland Security Department, was criticized for saying that DREAMers who hadn’t signed up for the Obama-era protections had been “too afraid” or “too lazy to get off their asses.”

However, even those who enlisted are vulnerable to deportation if their status runs out while they wait for the delay-plagued program to get through several layers of vetting before they can report to basic training.

Immigration experts and DACA advocates quickly pointed out that Mattis couldn't make such a guarantee without an executive order from the president, or legislation involving DHS.

“That's not up to DOD. It's up to DHS,” tweeted Arizona Democratic Rep. Ruben Gallego. “Once they step off base, there's nothing that Mattis or anyone else could do to protect DREAMers serving in our military from deportation,” referring to DACA recipients by a name drawn from the failed bipartisan DREAM Act, which would have provided undocumented migrants a path to citizenship.