Andrew Boyle works for the Liberty and National Security Program at the Brennan Center for Justice. He and Stewart start at the very beginning of a very current issue: What, precisely, constitutes a “national emergency?” Who gets to declare one? And what happens then?Specifically, can Donald Trump use the powers granted to the Executive during a national emergency to build his wall? He’ll face a fair amount of resistance, and Andrew and Stewart consider the various forms it might take.