He might have the authority to do so, but sure as hell some activist liberal judge will slap an injunction on it, and the case would take quite a while to wind it's way through the courts. Meanwhile, the border wouldn't be secure, so he's going to do something else. Damned if I know what that will be, though. Some say support for the wall is increasing lately, while others say it isn't. His SOTU address is coming up, and I'm guessing he wants to hammer the Dems on this issue with everybody watching.