I believe Texas had some clause in joining the federal government that allows them to bail. I would suspect other states could leave the union if push turns to shove and momentum grows in that direction.

However, everybody has wanted and continues to want to have their fingers in the federal pie, and that makes it much harder to pull away given how much everybody is now dependent on and intertwined with them.

But there is 1 interesting precedent being set: Legalization of marijuana. It is still federally illegal to use/possess/sell it, but states have rejected that and set their own standards. I don't think they can stop the feds doing raids within their borders, though, so it's not a total repudiation.