Well half of them outright won't for obvious reasons. And so what if a state says no? That doesn't change anything. He is now saying his word is above the legislative and judicial branch and all enforcement and regulatory powers of the federal government answer exclusively to his will.

This is America's Gleichschaltung. The president is now the absolute authority of the entire administrative state.

And then they'll lose federal funding for all sorts of things. The states will sue, possibly win, and Trump will say "make me", and the judiciary will sigh and say "we can't".