This is where Mr Trump’s talk of an “invasion” becomes more than rhetorical bombast. Framing the cartels as terrorists invading America is meant to legitimise his use of the law. And because America is being invaded, Mr Trump argues, he can block anyone from crossing the border. The courts may not see it that way. ■

The president’s Day 1 actions included directives that fly in the face of legal limits on involving the military in domestic operations and the constitutional guarantee of birthright citizenship.