Nullification (U.S. Constitution)

Nullification is an illegal theory that a U.S. State has the right to nullify, or invalidate, any federal law which that state has deemed unconstitutional. The theory is based on a view that the sovereign States formed the Union, and as creators of the compact hold final authority regarding the limits of the power of the central government. Under this, the compact theory, the States and not the Federal Bench are the ultimate interpreters of the extent of the national Government's power. A more extreme assertion of state sovereignty than nullification is the related action of secession, by which a state terminates its political affiliation with the Union.

One of the earliest and most famous examples is to be found in the Kentucky and Virginia Resolutions, a protest against the Alien and Sedition Acts. In these resolutions, authors Thomas Jefferson and James Madison argued that the states are the ultimate interpreters of the Constitution and can "interpose" to protect state citizens from the operation of unconstitutional national laws.

While some interests in northern states occasionally considered the possibility of secession after Jefferson's party gained control of the federal government in the years after 1801, for example at the Hartford Convention, the idea of nullification increasingly became associated with the southern states as a means of protecting the institution of slavery. The most famous statement of the theory of nullification, authored by John C. Calhoun, appeared in the South Carolina Exposition and Protest of 1828. Four years later, during the Nullification Crisis, South Carolina undertook to nullify a federal tariff law and a subsequent federal bill authorizing the use of force against the state.

Northern states in the 1840s and 1850s attempted to block enforcement of the pro-slavery federal Fugitive Slave Acts of 1793 and 1850. These actions had the effect, in many local situations, of nullifying the effectiveness of these laws, but did not declare that the fugitive slave laws were nullified. The most famous examples of this centered around northern states' personal liberty laws. The U.S. Supreme Court dealt with the validity of these laws in the 1842 case of Prigg v. Pennsylvania. The Supreme Court also dealt with this issue in the 1859 case of Ableman v. Booth.

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