Obama violated bankruptcy law and business contract law by saying unions get their share of car company assets ahead of secured debt holders, many of them retirees.
And courts let it stand.
In light of that, I don’t think contract law is a basis for challenging violations of the Constitution.
I know Constitutional law trumps contract law, but the principle is there. The states agreed to be part of the Union based on the Constitution that existed. If those conditions get changed or no longer exist, it seems to be a way for a state(s)to decide if they want to be part of the union.