Exactly who bombed the U.N. in Baghdad is the question everyone wants answered. But in some ways it misses a point that is already clear--that there is a growing abundance of potential suspects, ranging from radicalized locals to al-Qaeda emigres. What's worrisome is that they may be coalescing around the same cause, which is to turn Iraq into a showplace of terrorism.
For militants who share al-Qaeda's ideology, the target of the bombing was a natural one. For years, jihadists have reviled the U.N. as an arm of world infidelity. They have depicted the organization as a tool America relied on...