Ex-President Barack Obama is the mystery man of American politics. Given the absence of a viable paper trail, nobody can say for sure who he is. He manifests for us as a figure of multiple identities: a Christian, a Muslim, a secularist, a socialist, a humanist, an intellectual, a man of the people. His lack of definable substance, his inner absence, has been an important political advantage. As Obama himself confessed (or boasted) in The Audacity of Hope, this layering of anonymities enabled him to “serve as a blank screen on which people of vastly different political stripes project their...