Definition of National Emergency under the National Emergencies Act [March 1, 2019] [open pdf - 703KB]
From the Document: "States and various organizations have filed a number of lawsuits challenging President Trump's proclamation of a national emergency in order to secure funding for the construction of physical barrier along the U.S. southern border. The lawsuits assert that no national emergency exists and that the President has overstepped his authority. Some observers are concerned that the declaration of a national emergency under present circumstances will set a precedent for future presidents to declare national emergencies to override Congress on other policy matters. Others have raised alarm about the number of and nature of statutes that provide the President specific authorities once he has proclaimed a national emergency."
CRS Legal Sidebar, LSB10267
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html