We are a nation of underdogs. Three-quarters of those who came here arrived in some condition of unfreedom: as convicts, as indentured servants, as slaves. Yet this improbable immigrant mix somehow managed, against all odds, to field an army that defeated the greatest superpower of its age and to create a nation that became the envy of the world. Our affinity for underdogs, baked into our historic DNA, has been reinforced by the fairy tales and Bible...