Kansas lawmakers, declaring the federal government does not have the constitutional authority to regulate firearms in their state, were the latest to join the nullification movement with their May adoption of the Second Amendment Protection Act. This states' rights movement is called "nullification," and while enjoying a recent spike in popularity, is actually a procedural tool as old as the Constitution. It is based on one simple theory: The federal government exists by the will of the states. States, according to this thinking, have the right to decide which federal laws are constitutionally valid within their borders. A long history of court decisions--and the federal government's triumph in the Civil War--say otherwise.