 The enforcement of existing immigration law has never been contingent upon the passage of new. It's just not required. Title VIII gives any president all the authority. More specifically, Title VIII, Chapter 12, Subchapter 2, Part 2, Section 1182. I read the blurb over and over and over again. I won't bore you with it again. But it gives him plenty of potential control because he can, by proclamation, determine who is a non-documented or undocumented immigrant.