What principle allows states to invalidate federal laws they consider unconstitutional?

The principle that allows states to invalidate federal laws they consider unconstitutional is known as nullification. This concept is rooted in the belief that states have the right to reject federal laws that they believe overstep the bounds of the Constitution. Historical proponents of nullification argued that the Constitution is a compact among the states, which gives states a role in interpreting its meaning and limits. This idea was notably articulated during the early 19th century in debates over states' rights, particularly with the opposing views on federal authority and the power of state governments.

In contrast, secession refers to the act of withdrawing from the union rather than rejecting specific laws, making it a different action altogether. Federalism is a system of government where power is divided between the national and state governments, but it does not specifically endow states with the authority to invalidate federal legislation. Interposition, although related, is a more specific doctrine referring to a state’s right to step in between its citizens and the federal government, which doesn't directly address the broader concept of nullification as a means of invalidating laws.