Arlen Specter, a five-term senator from Pennsylvania, has just died, the AP reports. A Republican since 1965, he switched party affiliations in 2009 and ran as a Democrat, losing in the primary to Joe Sestak. After his defeat, Specter continued to teach law at the University of Pennsylvania, where last year he was named by the National Jurist one of the "23 professors to take before you die." He was 82.