The bombing of the London Underground last week prompted an outpouring of sympathy from Americans for their British allies. It also jolted many Americans into fretting about their own security. How vulnerable are they? Optimists think the danger is overdone. No significant act of terrorism has been carried out on American soil since September 11th 2001. That assault spurred vigilance. Passengers wishing to board aircraft must now queue to remove their shoes. Tougher cockpit doors keep would-be hijackers away from the controls. Stricter immigration rules, such as the requirement that young foreign males must reveal every country they have visited in the past ten years, screen out potential terrorists before they reach American territory.
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