Barack Obama began his presidency with an open hand toward the man he had just defeated in a race that was at times bitter. "There are few Americans who understand this need for common purpose and common effort better than John McCain," said Obama at an inauguration-eve tribute dinner to his former foe. But in the year since that evening of comity and collegiality, McCain has emerged as one of the leading critics of the new president. On foreign policy, his traditional area of expertise, and domestic affairs, where McCain has shown new passion, the 72-year-old Arizonan is making it...