Feb. 17 (UPI) — Acting Defense Secretary Patrick Shanahan said Saturday night he hasn’t decided how to divert money from the Pentagon to fund a border wall ordered by President Donald Trump’s national emergency declaration.

On Friday, Trump said he wants to move $6.7 billion, including $3.6 billion in military construction money and $2.5 billion in the military’s counter-narcotics activities, for barrier funding on top of $1.3 billion approved by Congress for security fencing along the Mexican border. The other funding includes $600 million in Treasury Department drug forfeiture funds.

Shanahan has final say on how much will be taken from which programs. In addition, he has authority to call up mobilized reserves to “perform a federal mission,” based upon Title 10 of U.S. Code, the Pentagon said in a statement Friday.

“I think I have a lot of discretion,” Shanahan told reporters on a flight from Munich to the United States on Saturday night. “You can trust the numbers in terms of the potential. Then you gotta marry it up with where the money would be spent.”

The U.S. Code also allows military construction funds to be moved to support other activities if the defense secretary determine they are “necessary to support the use of the armed forces.”

Also the Pentagon is authorized to use drug interdiction funding to support the Department of Homeland Security and doesn’t require Shanahan to prove a military need for the construction of “roads, fences and lighting.”

“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 told reporters aboard the military jet. “So very deliberately, we have not made any decisions.”

Shanahan said military housing is unlikely to be tapped.

“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. “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.”

Starting Sunday, Shanahan will receive a full briefing from the service secretaries potential programs where the money may be taken and other details after some initial planning.

“I’ll go in and review that analysis now that the emergency has been declared,” Shanahan said. “Based on that, we can do an assessment of what would be appropriate.”