“The people that say we create precedent — well, what do you have, 56, or a lot of times — well, that’s creating precedent, and many of those are far less important than having a border,” he said.
But several legal experts said there was another possible long-term consequence that had received less discussion: by violating that norm of self-restraint, Mr. Trump may prompt Congress to eventually take back some of that power from the presidency — at least in a post-Trump era, when a succeeding president might be willing, or believe that it is politically necessary, to sign such a bill.
Notably, Representative Jerrold Nadler, Democrat of New York and the chairman of the House Judiciary Committee, on Friday accused Mr. Trump of “a gross abuse of power that subverts the key principles laid out in the Constitution” over which branch controls the appropriation of funds, and announced an investigation. In 1976, it was the House Judiciary Committee that drafted the National Emergencies Act.
Stephen I. Vladeck, a law professor at the University of Texas, Austin, said that legislators may react to Mr. Trump’s move by enacting a new overhaul of those laws that tightened restrictions on when a president could use them.
Lawmakers could, for example, impose a strict definition of what qualifies as an emergency, taking away presidential flexibility to deal with unforeseen circumstances. Congress could also attach “sunset” clauses to emergency statutes, so that the president's special powers would automatically deactivate after a month or two without new action by lawmakers to extend them.
“The risk the president runs is that Congress will take away much, if not most, of the discretion it’s given to the president,” Mr. Vladeck said. “And then the concern is that Congress could hamstring a future president from having all the tools he or she might need to react to a future emergency. So a short-term win for the president could become a long-term loss for the presidency.”