Well, I think the Constitution is certain on this point. There is no clause that says a state cannot leave of its own accord. Since all powers not specifically granted to the Federal government are reserved to the states and the people, the answer lays right there: it is their decision.
Now what gets them in trouble is if they decide to fire upon the feds. At that point, they have declared war on the US and the US can respond in a similar fashion. Now, lets look around and note where the military bases of note are located. Hum, seems to me they are not located in the liberal states for the most part probably because they detest the military in the first place. No problem, they can have the Zero talk them back into the fold.
Vince
Vince