All President Trump has to do is declate the invasion of illegal immigrants for what it is, an invasion. Once he does that and declares Mexico a hostile foreign power for encouraging it then, as Commander-In-Chief, he has total authority to do anything necessary to secure the border, including building a wall or whatever else is necessary. Once the wall is built the US can settle all the bills and emminent domain issues/restitution after the fact. All the left can do is scream.
The first terrorist attack that happens after 1/20, Trump needs to declare a state of emergency and do what needs to be done to all enemies, foreign and domestic, on American soil.
This especially includes the scumbags in the press.