Few things are more difficult in politics than confronting failure and learning from it. It is especially difficult when a leader you have championed, and in whom you have placed your highest hopes, turns out to be less than he seemed. Such is the dilemma facing liberals in the age of Obama. Barack Obama entered the presidency with his sights and standards very high, and many liberals believed he could be the transformative figure they had been awaiting for generations. But by now it is clear that, by any reasonable measure (including those set out by Obama himself at the...