Nullification, in United States constitutional history, is a legal theory that a state has the right to nullify, or invalidate, any federal laws that they deem unconstitutional with respect to the United States Constitution (as opposed to the state's own constitution). There are similar theories that any officer, jury, or individual may do the same. The theory of state nullification has never been legally upheld by federal courts."[S]tates throughout U.S. history have attempted to use variations of the nullification doctrine to invalidate national law. However, every attempt by states to nullify federal law was clearly rejected by not only the federal government but also by other states." Card, Ryan (2010), "Can States 'Just Say No' to Federal Health Care Reform? The Constitutional and Political Implications of State Attempts to Nullify Federal Law", 2010 B.Y.U. Law Review 1795, 1808

The theory of nullification is based on a view that the states formed the Union by an agreement (or "compact") among the states, and that as creators of the federal government, the states have the final authority to determine the limits of the power of that government. Under this, the compact theory, the states and not the federal courts are the ultimate interpreters of the extent of the federal government's power. Under this theory, the states therefore may reject, or nullify, federal laws that the states believe are beyond the federal government's constitutional powers. The related idea of interposition is a theory that a state has the right and the duty to "interpose" itself when the federal government enacts laws that the state believes to be unconstitutional. Thomas Jefferson and James Madison set forth the theories of nullification and interposition in the Kentucky and Virginia Resolutions in 1798.

Courts at the state and federal level, including the U.S. Supreme Court, have repeatedly rejected the theory of nullification.Cases rejecting nullification, all of which are discussed in this article: Cooper v. Aaron, 358 U.S. 1 (1958) Bush v. Orleans Parish School Board, 364 U.S. 500 (1960) Ableman v. Booth, 62 U.S. 506 (1859) United States v. Peters, 9 U.S. (5 Cranch) 115 (1809) The courts have decided that under the Supremacy Clause of the Constitution, federal law is superior to state law, and that under Article III of the Constitution, the federal judiciary has the final power to interpret the Constitution. Therefore, the power to make final decisions about the constitutionality of federal laws lies with the federal courts, not the states, and the states do not have the power to nullify federal laws.

Between 1798 and the beginning of the Civil War in 1861, several states threatened or attempted nullification of various federal laws. None of these efforts were legally upheld. The Kentucky and Virginia Resolutions were rejected by the other states. The Supreme Court rejected nullification attempts in a series of decisions in the 19th century, including Ableman v. Booth, which rejected Wisconsin's attempt to nullify the Fugitive Slave Act. The Civil War ended most nullification efforts.

In the 1950s, southern states attempted to use nullification and interposition to prevent integration of their schools. These attempts failed when the Supreme Court again rejected nullification in Cooper v. Aaron, explicitly holding that the states may not nullify federal law.

The Constitution and the theory of nullification

Provisions of the Constitution

The Constitution does not contain any clause expressly providing that the states have the power to declare federal laws unconstitutional.

Supporters of nullification have argued that the states' power of nullification is inherent in the nature of the federal system. They have argued that before the Constitution was ratified, the states essentially were separate nations. Under this theory, the Constitution is a contract, or "compact", among the states by which the states delegated certain powers to the federal government while reserving all other powers to themselves. The states, as parties to the compact, retained the inherent right to judge compliance with the compact. According to supporters of nullification, if the states determine that the federal government has exceeded its delegated powers, the states may declare federal laws unconstitutional.Thomas Jefferson wrote in the Kentucky Resolutions of 1798: "[B]y compact, ... [the states] constituted a general government for special purposes, delegated to that government certain definite powers, reserving, each state to itself, the residuary mass of right to their own self-government. ... [E]ach party has an equal right to judge for itself, as well of infractions as of the mode and measure of redress." Nullification supporters argue that the power to declare federal laws unconstitutional not only is inherent in the concept of state sovereignty but also is one of the powers reserved to the states by the Tenth Amendment.The South Carolina Exposition and Protest of 1828, written by John C. Calhoun, stated: "[T]he power of the States to interpose in order to protect their rights ... like all other reserved rights ... is to be inferred from the simple fact that it is not delegated."

This view of the Constitution has been rejected by the federal courts, which consistently have held that under the Constitution, the states do not have the power to nullify federal laws. The courts have rejected the compact theory, finding that the Constitution was not a contract among the states. Rather, the Constitution was established directly by the people, as stated in the preamble: "We the people of the United States ..."In Martin v. Hunter's Lessee, 14 U.S. (1 Wheat.) 304 (1816), the Court said: "The Constitution of the United States was ordained and established not by the States in their sovereign capacities, but emphatically, as the preamble of the Constitution declares, by 'the people of the United States.' ... The [Articles of] Confederation was a compact between States, and its structure and powers were wholly unlike those of the National Government. The Constitution was an act of the people of the United States." See also McCulloch v. Maryland, 17 U.S. (4 Wheat.) 316 (1819) ("The government proceeds directly from the people [and] is 'ordained and established' in the name of the people. ... The Constitution, when thus adopted, was of complete obligation, and bound the State sovereignties.") and Texas v. White, 74 U.S. (7 Wall.) 700 (1869) (the union was "more than a compact"). The people made the federal government superior to the states in certain ways. Under the Supremacy Clause of Article VI, the Constitution and federal laws made in pursuance thereof are "the supreme law of the land ... anything in the constitution or laws of any state to the contrary notwithstanding."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." The courts have held that federal laws are therefore superior to state laws and cannot be negated by the states. Federal laws are valid and are controlling, so long as those laws were adopted in pursuance of—that is, consistent with—the Constitution. Determining whether a federal law is consistent with the Constitution requires interpretation of the law, which is inherently a judicial function. The federal judicial power granted by Article III of the Constitution gives the federal courts authority over all cases "arising under this Constitution [or] the laws of the United States".Article III provides that "The judicial power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties", and that "the Supreme Court shall have appellate jurisdiction" in such cases. The federal courts, therefore, have been given the power to determine whether federal laws are consistent with the Constitution, with the Supreme Court having final authority.See Marbury v. Madison, 5 US (1 Cranch) 137 (1803).

Thus, the federal courts have held that under the Constitution, federal law is controlling over state law, and the final power to determine whether federal laws are unconstitutional has been delegated to the federal courts. The courts therefore have held that the states do not have the power to nullify federal law.See Ableman v. Booth, 62 U.S. 506 (1859), Cooper v. Aaron, 358 U.S. 1 (1958).

The Constitutional Convention and state ratifying conventions The concept of nullification of federal law by the states was not discussed at the Constitutional Convention.According to a leading historian of the Constitutional Convention, nullification and the related concept of secession "were probably not even seriously considered at that time; there certainly is no record of their being mentioned in the convention". The records of the Constitutional Convention therefore do not provide support for the theory of nullification.

On the other hand, the records of the Convention support the idea that the power to declare federal laws unconstitutional lies in the federal courts. At least fifteen Constitutional Convention delegates from nine states spoke about the power of the federal courts to declare federal laws unconstitutional. For example, George Mason said that under the Constitution, federal judges "could declare an unconstitutional law void". James Madison said: "A law violating a constitution established by the people themselves, would be considered by the Judges as null & void."Ibid., p. 93. Elbridge Gerry said that the power of federal judges to interpret federal laws includes "a power of deciding on their constitutionality".Ibid., p. 97. See Prakash, Saikrishna, and Yoo, John, "The Origins of Judicial Review", 70 U. Chicago Law Review 887, 941–943, 952 (2003), which describes a number of statements in the Convention recognizing that the federal courts would have the power to declare laws unconstitutional. See also Judicial review in the United States.

Several of the Convention delegates said that the federal courts would have the power to determine disputes between the federal government and the states. Charles Pinckney referred to federal judges as "Umpires between the U. States and the individual States". John Rutledge indicated that the Supreme Court would "judge between the U.S. and particular states".Ibid., p. 428 These statements indicated that the Supreme Court would have final authority in constitutional disputes between the federal government and the states.