Nothing if, with the collaborationist GOP, they have the votes to override his veto. Of course, at that point, it is time for a general uprising against a government that is the declared enemy of Americans and is colluding with invaders bent on the destruction of the US.
If I assume anything anymore, it is that Congress will always try to act against the best interests of the nation. If they can harm us by screwing with Trump, they will.
FWIW, I think he needs to do a partial shutdown, wait thirty days, then start issuing pink slips till HE gets what WE need.