Budapest, 1956.Prague, 1968.Gdansk, 1981.Tianenmen Square, 1989.Tehran, 2009. Each of these surprise flashpoints in history’s long march against totalitarianism proved as dazzling at its outset as it did hopeless at its extermination. Each of them left a trail of broken bodies, but the last was different than all its historical forebears in one way: the president of the United States kept silent while it was unfolding. Barack Obama, and the world, saw police beat and gas protesters and kill 27-year-old music students and nine-year-old children; and Iranian reports indicate that those arrested were viciously tortured in a secret prison. All the...