The Federal government assumes that since the Federals won the Civil War, which was over States Rights vs Federal Rights and not over Slavery itself, that the Federal government trumps the States in all things. If Federal Law conflicts with State Law then the Federal Law wins. That may make sense in some areas such as Interstate Commerce or Military related Laws or Laws related to the National Border. However, the Federal govt has made the mistake of  interpreting the Supremacy of Federal Law over State Law in the wrong way.

The Federal government assumes that in ALL THINGS where there is a conflict between Federal wishes and States wishes that the Federal govt always has the upper hand.

What the Federal government either fails to recognize, intentionally chooses not to recognize or perhaps simply pretends not to know is that ultimately the States have authority over the Federal government. While extreme, the Constitution has even provided a direct Check and Balance over the Federal government which provides a means for the States to ultimately override a Federal government that has gone rogue and gotten out of control as an increasing number of people feel our current one has.

The States Have Ultimate Authority

(more at Disarm the Government)