The stage might have belonged to U.S. Sen. Timothy M. Kaine, but the class belonged to professor Larry J. Sabato. That, however, is about to change. While Kaine explained his heart change on same-sex marriage to the 400-plus students at the University of Virginia’s “Introduction to American Politics” course, Sabato sat on a folding chair offstage for the last time. “I’ve been doing the beginning class for 35 years and, to be honest, as you get older, you just don’t have the energy you used to have and this class takes a lot of energy,” Sabato said as s...