by Caleb Nelson

Emerson G. Spies Distinguished Professor of Law at the University of Virginia School of Law


When the Philadelphia Convention got under way in May 1787, Governor Edmund Randolph of Virginia presented what has come to be known as “the Virginia plan”—a collection of resolutions forming a blueprint for the Constitution. As amended a few days later, one of the resolutions included the following proposal: “the National Legislature ought to be imit is provided ... to negative all laws passed by the several States, contravening in the opinion of the National Legislature the articles of Union,or any treaties subsisting under the authority of the Union.”

At first, supporters of this idea seemed optimistic about its chances. In early June, indeed, Charles Pinckney and James Madison moved to extend the proposed congressional “negative” so as to reach all state laws that Congress deemed “improper.” This motion, however, went down to defeat. The next month, over Madison’s objections, the Convention rejected the narrower version of the power too. In place of the proposed congressional “negative,” the Convention approved a precursor of the Supremacy Clause. That Clause went through various changes in the ensuing months, but the final version says:

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.

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Instead of giving Congress additional powers, the Supremacy Clause simply addresses the legal status of the laws that other parts of the Constitution empower Congress to make, as well as the legal status of treaties and the Constitution itself. The core message of the Supremacy Clause is simple: the Constitution and federal laws (of the types listed in the first part of the Clause) take priority over any conflicting rules of state law. This principle is so familiar that we often take it for granted. Still, the Supremacy Clause has several notable features.

To begin with, the Supremacy Clause contains the Constitution’s most explicit references to what lawyers call “judicial review”—the idea that even duly enacted statutes do not supply rules of decision for courts to the extent that the statutes are unconstitutional. Some scholars say that the Supremacy Clause’s reference to “the Laws of the United States which shall be made in Pursuance ” itself incorporates this idea; in their view, a federal statute is not “made in Pursuance ” unless the Constitution really authorizes Congress to make it. Other scholars say that this phrase simply refers to the lawmaking process described in Article I, and does not necessarily distinguish duly enacted federal statutes that conform to the Constitution from duly enacted federal statutes that do not. But no matter how one parses this specific phrase, the Supremacy Clause unquestionably describes the Constitution as “Law” of the sort that courts apply. That point is a pillar of the argument for judicial review. In addition, the Supremacy Clause explicitly specifies that the Constitution binds the judges in every state notwithstanding any state laws to the contrary.

The Supremacy Clause also establishes a noteworthy principle about treaties. Under the traditional British rule, treaties made by the Crown committed Great Britain on the international stage, but they did not have domestic legal effect; if Parliament wanted British courts to apply rules of decision drawn from a treaty, Parliament needed to enact implementing legislation. The Supremacy Clause breaks from this principle. Subject to limits found elsewhere in the Constitution, treaties are capable of directly establishing rules of decision for American courts.

This aspect of the Supremacy Clause reflected concerns that individual states were jeopardizing the fledgling nation’s security by putting the United States in violation of its treaty obligations. For instance, at the end of the Revolutionary War, Article IV of the Treaty of Peace between the United States and Great Britain had specified that “creditors on either side<> shall meet with no lawful impediment to the recovery of the full value in sterling money, of all bona fide debts heretofore contracted.” Nonetheless, several states enacted or retained debtor-relief laws whose enforcement against British creditors would violate this promise, and British diplomats argued that these violations excused Britain’s own failure to withdraw all armies and garrisons from the United States. The Supremacy Clause responded to this problem: just as state courts were not supposed to apply state laws that conflicted with the Constitution itself, so too state courts were not supposed to apply state laws that conflicted with Article IV of the Treaty of Peace. Indeed, the peculiar wording of the Supremacy Clause—covering treaties already “make ... under the Authority of the United States” as well as treaties that “shall be made” in the future—was specifically designed to encompass pre-existing agreements like the Treaty of Peace. While modern scholars have debated the circumstances in which treaties should be understood to establish rules of decision for cases in American courts, the Supremacy Clause unquestionably makes such treaties possible.

Under the Supremacy Clause, the “supreme Law of the Land” also includes federal statutes enacted by Congress. Within the limits of the powers that Congress gets from other parts of the Constitution, Congress can establish rules of decision that American courts are bound to apply, even if state law purports to supply contrary rules. Congress also has at least some authority to put certain topics wholly off limits to state law, or otherwise to restrict what state law can validly say about those topics. As long as the directives that Congress enacts are indeed authorized by the Constitution, they take priority over both the ordinary laws and the constitution of each individual state. (During the ratification period, Anti-Federalists objected to the fact that federal statutes and treaties could override aspects of each state’s constitution and bill of rights. But while this feature of the Supremacy Clause was controversial, it is unambiguous.)

In modern times, the Supreme Court has recognized various ways in which federal statutes can displace or “preempt” state law. Some federal statutes include express “preemption clauses” forbidding states to enact or enforce certain kinds of laws. A few other federal statutes have been interpreted as implicitly stripping states of lawmaking power throughout a particular field. But even when a federal statute does not contain an express preemption clause, and even when the statute does not implicitly occupy an entire field to the exclusion of state law, the directives that the statute validly establishes still supersede any conflicting directives that the law of an individual state might purport to supply.

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Every year, courts decide an enormous number of cases that involve whether a particular federal statute should be understood to preempt a particular aspect of state law. Often, the key disputes in these cases boil down to questions of statutory interpretation. (If the relevant federal statute includes a preemption clause, what does the clause mean? Should any additional instructions about preemption be inferred? And what is the precise content of all the other legal directives that the statute establishes, whether expressly or by implication?) But apart from disputes about what the relevant federal statute should be understood to say and imply, and apart from any disputes about whether the Constitution really gives Congress the power to say and imply those things, some preemption cases may implicate disagreements about the Supremacy Clause itself. Of course, the basic principle that valid federal statutes preempt conflicting rules of state law is not controversial. But different judicial opinions suggest different views about what counts as a conflict for this purpose, and some of those disagreements may grow out of the Supremacy Clause: while there is no doubt that the Supremacy Clause sometimes requires courts to disregard rules of decision purportedly supplied by state law, there is room for debate about the precise trigger for that requirement.