 His executive orders on immigration were challenged, and the Supreme Court validated his final iteration of the Muslim ban, saying, of course an executive can decide who is an existential threat to this country and who isn't. And, in fact, if Trump was in office right now, he'd be able to close the border. It says you can do it. Of course you can do it. There's a congressional enactment that allows it. The executive powers to faithfully execute the laws allow it.