The Duke of Wellington once defined the best test of a leader. His idea might be helpful to an organization presently needing a bit of help from a wise old head: the Democratic Party. The best test of a general, he wrote, was “to know when to retreat, and to dare to do it.” He knew what he was talking about, because he executed the most successful retreat in British history, from the battle that he had won in the summer of 1809 at Talavera in central Spain to the Lines of Torres Vedras that he had fortified just outside...