Douthat has tried something very brave in this concise and original book: he draws a link between some of the ills in American politics and culture and the decline of orthodox Christian belief since the post–World War II heyday of figures such as Archbishop Fulton Sheen and the theologian Reinhold Niebuhr. American religion is a complicated subject, and Douthat’s knowledge of Protestant denominational and theological details sometimes fails him. But his strong core argument is that Niebuhr was right: when American Christianity loses its grip on the idea of original sin, it rapidly falls victim to cultural fads and nationalist pride. Belief in the perfectibility of man leads to unreasoning optimism in the United States’ capacity to change both itself and the world; when these unrealistic hopes are not realized, Americans quickly turn to an equally unreasoning despair and fall prey to apocalyptic forebodings. Douthat sees this syndrome at work on both the left and the right today and argues that healthier political debate requires a reengagement with orthodox Protestant and Catholic ideas.