Earlier today, the Vox website posted a symposium in which a variety of legal commentators (myself included) consider the legality of President Trump's effort to use emergency powers to build his border wall. Most conclude that, while Trump may have the authority to declare a national emergency, that does not give him the power to spend money and condemn property to build the wall.
Here is an excerpt from my contribution:
This plan is illegal, and would set a dangerous precedent if it succeeds. Article I of the Constitution mandates that "No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law." Only Congress has the power to make such laws. This vital rule ensures no one person can seize control of the nation's public funds.
To get around Congress, Trump seeks to use emergency powers. Under the poorly structured National Emergencies Act of 1976, Trump may indeed be able to declare an emergency at the border, even though there is no genuine crisis there. But it does not follow that he can therefore appropriate money for the wall. The NEA does not give him unlimited authority, but only a specific set of powers. None of them are broad enough to justify spending money on a border wall....
Even if Trump can use an emergency declaration to get the money he wants, that is not enough to build the wall. He also needs the authority to use eminent domain to seize land from numerous unwilling owners. Such authority must be expressly authorized by the legislature; it cannot simply be inferred. And there is no such clear authorization here.
Trump's attempt to use emergency powers is virtually certain to be challenged in court. While he deserves to lose, it is possible he could prevail, in part because courts often give the president undue deference on immigration and national security issues.
Should he win, it would set a very dangerous precedent. Future presidents, too, could use it to appropriate money and seize private property without congressional authorization, especially if there is some national security pretext for doing so.....