Interposition is a dubious and hotly contested concept within the framework of federalism in the United States that posits a state has the right to interpose itself between its citizens and the federal government when it believes a federal law is unconstitutional. Essentially, it argues that individual states have veto power over any laws passed by the federal government.

The doctrine is rooted in the belief that the state governments retain certain sovereign powers, despite the supremacy clause of the U.S. Constitution, which asserts the supremacy of federal law over state laws. Advocates of interposition argue that because the states were instrumental in the creation of the federal government, they possess the authority to contest federal overreach and protect the rights and liberties of their citizens. This doctrine gained prominence in the 19th century and was notably invoked in the 1950s and 1960s by some Southern states in opposition to desegregation and civil rights legislation, under the guise of states’ rights.

However, the doctrine of interposition has been highly controversial and widely debated within legal and political circles. The U.S. Supreme Court has consistently rejected the notion that states can unilaterally declare federal laws unconstitutional and nullify them. In cases such as Cooper v. Aaron (1958), the Court reaffirmed the supremacy of federal law, emphasizing that states do not have the authority to disregard federal mandates.

Despite this, the concept of interposition periodically resurfaces in political discourse, particularly in contexts where state and federal laws are in conflict, such as environmental regulations, gun control, and health care. While the legal standing of interposition is largely settled, it remains a symbol of the ongoing debate over the balance of power between state and federal governments.