Trump should order the Pentagon to start building the wall

But many legal scholars say there is a way Trump could act legally. Current law allows the Defense Department to use “un-obligated” money to fund construction projects during war or emergencies. “The Department of Defense has funds in its account that are not specifically designated for anything,” Harvard Law School professor Mark Tushnet told NBC News. “My instinct is to say that if he declares a national emergency and uses this pot of unappropriated money for the wall, he’s on very solid legal ground.”

But Trump would be on shakier ground — even with his conservative base — if he pursued his concept of a “military version of eminent domain.” Legal analysts don’t know if such a concept is firmly rooted in the law even during peacetime. Seizing land along the border would also create many opportunities for abuse. The federal government owns less than one-third of the land adjoining Mexico. The rest belongs to local governments, Native American tribes, and private-property owners.