ONBOARD A US MILITARY AIRCRAFT — Acting Secretary of Defense Patrick Shanahan said Saturday he had made no decisions on whether the border wall was militarily necessary, a key determination required before military construction funds could be redirected to build it.

On Friday, President Donald Trump announced he would get a border wall built by declaring a national emergency, which allows his administration to access unspent funds in defense accounts. The White House has eyed $3.6 billion in military construction funds, drawing concern from lawmakers and the services.

Shanahan is expected to ultimately support the wall construction, but he is still determining how military spending could support it.

“We understand there are some priorities that won’t be considered,” Shanahan said. “Military housing ... what’s been interesting … I’ve received a number of letters, I’ve had lots of feedback. ‘Do not jeopardize the projects that are underway,’” Shanahan said. “[Navy] Secretary [Richard] Spencer, so many people, they are very mindful about it, and I appreciate we’re trying to work through this very complicated situation. People remind us, these are real, live, very important projects.”

Shanahan will be briefed by the service secretaries this week on the issue. He will also get an assessment Sunday from the Joint Chiefs of Staff on potential options to respond to the national emergency declaration, to include “where barriers should be prioritized from a military perspective,” a defense official told reporters traveling with Shanahan.

Section 2808 of Title 10 of U.S. Code allows military construction funds to be reprogrammed to support other activities, such as Trump’s national emergency declaration, if there is a determination they are “necessary to support the use of the armed forces,” the Pentagon said in a statement. Shanahan said he has made no decisions on that issue.

“We always anticipated that this will create a lot of attention, and since monies could potentially be redirected, you can imagine the concern this generates,” Shanahan said. “So very deliberately, we have not made any decisions.”

The suggestion that military construction funds could be used angered some members of Congress and advocacy groups, who noted that just days before, the Army Secretary and Army Chief of Staff, Gen. Mark MIlley, who is tapped to be the next chairman of the Joint Chiefs, had vowed to do better following explosive reports on the shoddy construction and decrepit living conditions facing some soldiers and their families.

In his on-camera interview, Shanahan suggested that military housing in particular would be protected, and a defense official after the interview confirmed Shanahan had communicated to concerned lawmakers that military family housing funds would not be touched.

However, there are other pots of funding DoD could use that would not require Shanahan to justify a military need.

In a one-page statement Friday on DoD authorities, the Pentagon said it is authorized to use drug interdiction funding to support the Department of Homeland Security, which does not require Shanahan to prove a military need before that funding could be used for the construction of “roads, fences and lighting,” the Pentagon said in a statement.

The White House said Friday it had identified $2.5 billion in available DoD counter-drug operations funding that could be used.