Article VI Section2 reads in part,
This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land...
Any law not made IN PURSUANCE of the Constitution, like Obamacare, is NOT the Law of the Land. The states need to understand that and be ready to fight for it.
Point out where the Constitution says the state has the right to decide that.