The Supremacy Clause provides: “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; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the contrary notwithstanding.” Art. VI, cl. 2. This language translates into a fundamental principle of our constitutional system of government: State law must conform to the dictates of the Constitution, and yield to constitutionally valid federal law whenever a conflict between the two arises. To conclude otherwise would be to permit each individual state to control what the Constitution defines as the business of the nation as a whole.
The judicial foundation for the law of federal supremacy can be traced to two opinions by Chief Justice John Marshall, McCulloch v. Maryland, 17 U.S. (4 Wheat.) 316 (1819), and Gibbons v. Ogden, 22 U.S. (9 Wheat.) 1 (1824). While neither opinion breaks ground beyond that which should be evident from the text of the Supremacy Clause, both opinions affirm, with confident and enduring rhetoric, the principle of federal supremacy within the sphere of constitutionally granted federal powers. The essence of that principle is that no state may transgress the norms of the Constitution or interfere with the constitutional exercise of federal authority.
At issue in McCulloch v. Maryland was the authority of a state to impose a tax on the Second Bank of the United States, a federally chartered institution. The first part of Marshall’s opinion upheld the power of Congress to charter the bank. See §5.2. Given that conclusion, the question was whether a state could nonetheless impose a tax on this constitutionally created institution. Marshall described the basic principles of federal supremacy in the introductory section of his opinion:
If any one proposition could command the universal assent of mankind, we might expect it would be this: that the government of the Union, though limited in its powers, is supreme within its sphere of action. This would seem to result necessarily from its nature. It is the government of all; its powers are delegated by all; it represents all, and acts for all. Though any one State may be willing to control its operations, no State is willing to allow others to control them. The nation, on those subjects on which it can act, must necessarily bind its component parts. But this question is not left to mere reason: the people have, in express terms, decided it, by saying, “this constitution, and the laws of the United States, which shall be made in pursuance thereof,” “shall be the supreme law of the land,” and by requiring that the members of the State legislatures, and the officers of the executive and judicial departments of the States, shall take the oath of fidelity to it.