General Discussion

This principle of “anti-commandeering” dates back to the 1842 Supreme Court decision Prigg v. Pennsylvania, in which the justices ruled that local and state law enforcement agencies could not be compelled to enforce the Fugitive Slave Act.

In short: the state is tasked with enforcing state laws; the federal government is tasked with enforcing federal laws. States cannot formally nullify federal law, nor can they block federal agents from operating within their borders--but they cannot be forced by the federal government to enforce federal laws.

Of course, due to the Supremacy Clause of the Constitution, federal laws and treaties made under the authority of the United States constitute the "supreme Law of the Land", and thus take priority over any conflicting state laws.