Barack Obama is often described as some kind of Niebuhrian, a tag he has encouraged by describing Reinhold Niebuhr as a major influence on his thought. Niebuhr was a complex figure who prized ambiguity and paradox, changed his positions many times, and found his way by reacting pragmatically to events—all of which may turn out to be true of Obama. But the key to Niebuhr, and to Obama’s interest in him, is the idea of combining a realistic understanding of politics and human nature with a religiously inspired idealism. Had Niebuhr lacked the humility and intellectual flexibility to change his mind numerous times, he would not have become the leading American Christian public intellectual of the twentieth century. [...]