Is there an irreconcilable disparity between authentic Christian faith and hard-boiled political realism? Common sense seems to require an unequivocal “yes”—one is so different from the other as to preclude any coherent combination of them. Yet we can find such a combination, or a significant approximation of it, in the philosophy of Reinhold Niebuhr. And that is what makes him an intriguing thinker and commentator on public affairs. Much of Niebuhr’s extensive writing, newly collected by the Library of America, is focused upon the role and limits of morality in politics, especially international politics. He is critical of “realists” who would…