Many of the career lawyers in the DOJ would resign in protest.
ICE agents-- the ones on the front lines who have to enforce the EO-- might enforce it or they might not. If they did, the federal court would probably hold some ICE agents in contempt in order to scare the rest of them. Trump and the federal courts would then be issuing conflicting orders to the U.S. Marshals, resulting in more resignations and more chaos.
The Democrats in Congress would immediately introduce an impeachment resolution, and some Republicans of the McCain-Graham wing would join them.
In short, we would quickly find ourselves living in "interesting times."
Also, he needs to channel Bill kinton and fire the DOJ attorneys en-masse.