As I drove up U.S. Highway 280, swerving in and out of traffic and making my way from suburban Birmingham toward the city’s center, I thought about the events of the past year that had led up to this moment. For many months the hottest rumor in Alabama politics was that Governor Robert Bentley had engaged in a long-running extramarital affair with his senior political advisor Rebekah Mason, a married mother of three. At first the idea seemed so absurd I dismissed it as politically motivated nonsense. Now, here I was, driving toward an obscure Birmingham gas station to obtain...