"All questions of power, arising under the constitution of the United States, whether they relate to the federal or a state government, must be considered of great importance. The federal government being formed for certain purposes, is limited in its powers, and can in no case exercise authority where the power has not been delegated. The states are sovereign; with the exception of certain powers, which have been invested in the general government, and inhibited to the states. No state can coin money, emit bills of credit, pass ex post facto laws, or laws impairing the obligation of contracts, &c. If any state violate a provision of the constitution, or be charged with such violation to the injury of private rights, the question is made before this tribunal; to whom all such questions, under the constitution, of right belong. In such a case, this court is to the state, what its own supreme court would be, where the constitutionality of a law was questioned under the constitution of the state. And within the delegation of power, the decision of this court is as final and conclusive on the state, as would be the decision of its own court in the case stated."
Justice John McLean
(1785-1861) U. S. Congressman for Ohio (1813-16), U.S. Postmaster General, Associate Justice of the U.S. Supreme Court (1830-61), presidential candidate for the Whig and Republican parties
Craig v. Missouri, 4 Peters 410 (1830) [29 U.S. 410, 464]