James Madison on states' rights

The Constitution of the United States was formed by the sanction of the States, given by each in its sovereign capacity. It adds to the stability and dignity, as well as to the authority of the Constitution, that it rests on this solid foundation. The States, then, being parties to the constitutional compact, and in their sovereign capacity, it follows of necessity that there can be no tribunal above their authority to decide, in the last resort, whether the compact made by them be violated; and, consequently, as parties to it, they must themselves decide, in the last resort, such questions as may be of sufficient magnitude to require their interposition.

~ James Madison, Virginia Resolutions