They could refuse to turn over that portion of the federal income taxes collected in their state that would go to fund this crap... that would bring things to a head pretty quicklike.
I also hope the governors get together and plan measured resistance. The states, which granted limited powers to their creation, the federal government, have long had their retained powers abused by radical judges and Leftist looney tunes like Pelosi/Reid/Obama.
It is time for the states to challenge our tyrannical federal government.