Here is the fun part - POTUS is under no obligation to abide by the court rulings of a district court. The injunction would need to come from SCOTUS, as I understand, before it truly becomes "lawful."
You are in the military and the President just ordered the wall to be built. You say: "nah… Don't wanna." You're fired. A DC district court files an injunction. You say "nah, I can't." You're reassigned. Rinse and repeat until SCOTUS actually files an injunction.
Wait… Where is RBG?