From the editorial board of the Wall Street Journal:
With Democrats in Congress refusing to appropriate $5.7 billion for a border wall, President Trump now says he may declare a national emergency. He’s probably right that he has the legal authority, but it would set a bad precedent that conservatives who believe in the separation of powers could live to regret.
Lower courts may enjoin a national emergency declaration, and Mr. Trump could then blame liberal judges for blocking his wall. But appellate courts might establish new constraints on executive power that circumscribe a President’s response to future crises. There’s no guarantee the Supreme Court would hear the case.
If Mr. Trump did win in court, a President Elizabeth Warren might take the precedent as license to circumvent Congress whenever it is politically expedient. Rising carbon emissions or even income inequality could be declared national emergencies. The media would cheer them on.