Vice President Mike Pence said Monday that White House lawyers are still looking into the legality of President Donald Trump declaring a national emergency to construct a $5.7 billion wall along the U.S.-Mexico border.

Trump will give a national address from the Oval Office Tuesday at 9 p.m. Eastern Time, during which he’s expected to discuss the partial government shutdown continuing over a Congressional impasse on the wall. Trump also plans to visit the southern border Thursday, according to a tweet from White House press Secretary Sarah Sanders.

The announcements come on the heels of Trump’s statements to reporters Friday saying he could end the legislative stalemate on border wall construction by declaring a national state of emergency, an option he said he would consider using depending on the progression of negotiations with Democratic lawmakers.

"I can do it if I want," the president told reporters. "We can call a national emergency because of the security of our country. We can do it. I haven't done it, I may do it."

Trump is right. He can declare a national emergency. Yet funding for wall construction, as a national emergency, presents thornier legal hurdles.

The National Emergencies Act of 1976 is the underlying law that allows presidents to carry out emergency actions. In order to use it, a president must couple it with a separate, existing law that authorizes funds for emergency use. The Act was created following the Nixon Watergate scandal to rein in executive power, ending decades of presidential overreach and terminating existing emergency authority.

“Once he [declares an emergency], he must make the decision public, and he must also specify which laws he's drawing on for his emergency powers,” Kim Lane Scheppele, professor of international affairs at Princeton University, told Yahoo Finance, outlining the steps the president must take to use the Act to fund a wall.

The framework, Scheppele said, gives rise to two questions with respect to Trump’s state-of-emergency scenario: 1) whether any emergency power can be found somewhere in an already-existing law that could be stretched to move funds appropriated for one purpose to use for another; and 2) whether any transferred funds would be permitted in a context involving either immigration or border protection.

Needle in a statutory haystack

“Unknown to most Americans, a parallel legal regime allows the president to sidestep many of the constraints that normally apply,” a report from The Atlantic states. “The moment the president declares a ‘national emergency’ — a decision that is entirely within his discretion — more than 100 special provisions become available to him.”

As it turns out, more than 400 provisions buried within existing laws give a president authority to take special action during declared emergencies.

“Nobody knows exactly how many there are across the entire U.S. code,” Scheppele said. “The Congressional Research Service’s last estimate was that some 400 plus statutes included emergency provisions, so there are many options to choose from.”

“I would guess that the White House legal counsel’s office is working overtime to go through each of these laws looking for something that can be used for this purpose,” Scheppele said, adding that the office should have a list of laws that include emergency provisions.

So far, Scheppele and her colleagues identified at least two such laws that the administration might be able to use to form a “non-trivial” basis for border wall funding.

The first, 33 U.S.C. 2293, permits the Secretary of Defense to direct the Army’s civil works program to redirect funds to “construct or assist in the construction, operation, maintenance, and repair” of projects that are “essential to the national defense.”

Another statute, 10 U.S.C. 2808, permits the Secretary of Defense to direct military programs to redirect appropriated funds to undertake military construction projects.

“Whether a wall is military or civilian depends on the reasons for its construction,” Scheppele said.

“There’s just all kinds of emergency provisions hiding throughout the U.S. Code,” she added.

The fiscal year’s budget appropriation for military construction totals $10.3 billion, of which slightly more than $2 billion has already been allocated to construct education, housing, and medical use facilities. Appropriations for the Army’s civil works program total $7 billion for the fiscal year.

Legally sound?

Yale Law professor Bruce Ackerman argued in a New York Times op-ed that use of the U.S. military and defense funds to build a border wall would amount to a criminal act for both for the president, and for military members who carry out such orders.

“I told him he was wrong [yet brilliant],” Scheppele said. “The whole provision of the National Emergencies Act that Bruce relies on is no longer valid.”

Scheppele is talking about a 1983 Supreme Court case, Immigration and Naturalization Service v. Chadah, that overruled a section in the Act that allowed Congress to override the executive branch.

Other legal scholars argue that a 1952 Supreme Court decision during President Harry Truman’s administration governs the funding of actions proposed by presidents during times of emergency. Youngstown v. Sawyer held that an executive order directing the Secretary of Commerce to seize U.S. steel mills to prevent a nationwide strike during the Korean War required approval from Congress.

The Youngstown decision, which predates the 1976 Act, has played out more as an exception than as a rule, as presidents have used emergency declarations to carry out emergency actions from internment of Japanese descendants during WWII, to warrantless wiretapping post-September 11 attacks.

The partial government shutdown impact

The administration’s other tall order is finding a law that operates within a government department still funded during the partial government shutdown.

“Defense has been funded during the partial government shutdown,” Scheppele said. “But Homeland Security is one that hasn’t been funded. “So if I were Trump, I wouldn't look at Homeland Security because (depending on which fiscal year they’re looking at) they ran out of money.”

Also key to an emergency declaration-based border wall is how the administration characterizes the emergency.

“If the president continues to make the case that the wall is necessary to prevent terrorists from entering the U.S., then he may be able to make the case that building a wall has a military purpose and he has a freer hand,” Scheppele said.

According to Scheppele,, a third, though less likely, statute that could justify border wall funding is 28 CFR Part 65, which allows the federal government to compensate border states for management of immigration issues. Because the law’s fund has only $20 million at present, Scheppele says its prospects as a wall purse are slim.

Yahoo Finance reached out to the U.S. Justice Department seeking a list of statutes containing provisions on presidential emergency declarations and did not receive an immediate response.

Alexis Keenan is a New York-based reporter for Yahoo Finance. She previously produced live news for CNN and is a former litigation attorney. Follow her on Twitter at @alexiskweed

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