THE THWARTED Christmas Day airplane bombing raises three causes for alarm. First, it illustrates a screening system that remains porous enough to let a suspect board with the same explosive shoe-bomber Richard Reid attempted to use in 2001. Second, it exposes a terrorism bureaucracy too clumsy to catapult the suspect, Umar Farouk Abdulmutallab, at least to a higher level of preflight scrutiny after his father came forward with warnings that he might pose a danger. Third, if it is true that the suspect received explosives training from al-Qaeda in Yemen, the incident underscores the emergence of that troubled nation as...