Walter McDougall is America’s greatest living historian. His The Heavens and the Earth: A Political History of the Space Age (1985) earned him the Pulitzer Prize. His Promised Land, Crusader State (1997) summarized American foreign policy from the founding to our own time while explaining twentieth-century statesmen’s radical departures from their predecessors. In Freedom Just around the Corner: A New American History, 1585–1828 (2004) and…