In addition to 15 years as a U.S. senator, John C. Calhoun of South Carolina served as president of the Senate (vice president of the U.S.). He was a key figure in the Senate's Golden Era, a period in Senate history marked by heated debates over slavery and territorial expansion. Calhoun was the Senate's most prominent states' rights advocate, and his doctrine of nullification professed that individual states had a right to reject federal policies that they deemed unconstitutional. When a 1957 Senate committee announced that Calhoun had been selected as one of the Famous Five, chairman John F. Kennedy praised Calhoun for being a "forceful logician of state sovereignty" and a "masterful defender of the rights of a political minority against the dangers of an unchecked majority."