Few people come as quickly to the defense of George McGovern as McGovern himself. The antiwar senator from South Dakota lost to Richard Nixon in a landslide in the 1972 presidential election, only to see Nixon, caught up in the Watergate scandal, resign in disgrace. For McGovern, though—along with many Democrats who followed him—the damage was done, and the now retired politician has spent decades defending the electability of antiwar liberals, insisting his campaign was undone by dirty tricks and bad luck. In recent years, McGovern, 86, hasn't relinquished the spotlight, condemning the war in Iraq and declaring Barack Obama,...