Acting defense secretary Patrick Shanahan said Saturday he would soon start to examine projects that could be delayed or canceled to free up funds for border reinforcement.

Speaking to reporters at the close of his first overseas tour since becoming Pentagon chief last month, Shanahan said the military’s Joint Staff had been conducting a “mission analysis” on ways to deal with drugs and migrants at the border. “Based on that, we can do an assessment of what would be appropriate,” he said.

Shanahan said the department had been preparing for weeks for a potential emergency declaration.

President Trump on Friday declared a national emergency in an attempt to circumvent Congress and redirect taxpayer money to fund hundreds of miles of barriers along the U.S.-Mexico border.

A defense official, speaking on the condition of anonymity to discuss internal planning, said the military’s analysis included an assessment of where border barriers would be most effective in consideration of national security.

Shanahan said he had leeway to determine a final figure from available funds that would be used for border-related activities — $3.6 billion from designated military construction funds. He said service secretaries would be involved in identifying affected projects.

“All of this money has been assigned for different purposes, so it comes down to: What are you going to trade off?” he said.

The defense official said it was likely though not certain that the Pentagon would devote the entire $3.6 billion pool of identified military construction funds to the border.

Shanahan said certain projects would not be considered, including military housing.

“We are following the law, using the rules,” he said. “We’re not bending the rules.”

White House officials plan to use $8 billion to build fencing they say will block or discourage more immigrants.

Of that money, $1.375 billion was approved by Congress on Thursday, to be allocated for 55 miles of “pedestrian fencing” along the border in southern Texas.

The White House plans to use $600 million from the Treasury Department’s forfeiture funds account, which contains money seized by the federal government from illicit activities.

An additional $2.5 billion would be redirected from a Pentagon program for countering drug activity, and $3.6 billion would be moved from military construction accounts.

It is the final pot of money that White House officials said required a national emergency declaration; the White House is generally barred from moving money from one account to another without congressional approval.

Trump promised during the 2016 campaign that Mexico would finance a border wall. Since becoming president, however, he has insisted the money should come from U.S. taxpayers.

Damian Paletta, Mike DeBonis, John Wagner and Amy B Wang contributed to this report.