One of the scarier aspects of the Spain bombing, particularly if it’s Al Qaeada, is that it shows they can abandon their love of airplanes. For years I’ve been wondering when it was Al Qaeda would discover commuter trains, and I know I’m not alone. The DC-New York-Boston Amtrak alone would make for a crippling target and, as best I can tell, people can just walk on with a steamer truck of plastic explosives.