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. ■

President Donald Trump's administration has directed U.S. prosecutors to criminally probe local officials who resist immigration enforcement efforts, intensifying a sweeping crackdown that Trump launched the day he took office.