There is an unreal, artificial aspect of systems to warn the public about terrorist threats, the latest U.S. version of which the Department of Homeland Security announced this week. But American attitudes toward terrorism make some such system a political necessity. The public expects the government to be on top of terrorist threats, and a warning system is one way to look like it is. The public also wants to feel it is being kept informed rather than being kept in the dark. Such systems cater to the notion that a well-functioning government security apparatus ought to be able to recognize and to counter any terrorist threat.
So for the foreseeable future there will be some such public warning arrangement, with each version designed to mitigate the principal complaints about the previous one. The current version discards the much-maligned stoplight chart with its five color-coded levels of threat. In response to observations that the threat level in the old system rarely seemed to change, the new system incorporates a sunset provision that leads to cancellation of a warning after a predetermined period unless it is specifically renewed.
No amount of tinkering with the design can overcome the inherently self-negating element of any such warning system. If the authorities had detailed enough information to satisfy the public yearning for specificity, they probably would have detailed enough information to roll up the plot and preclude any warning at all. Even if the information is semi-specific regarding possible targets, there still is a self-negating element; a public warning that narrows the threat to certain types of targets is a cue to the terrorists to aim at a different target.