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.

The sunset clause would seem to make sense, but there is a partial phoniness about that, too. Timing is only one type of possible information about terrorist plots. It does not speak directly to the credibility of other types of information. If the specified time period comes and goes without an attack, we are left to wonder whether the information about timing was inaccurate, or the plotters adjusted their plans in response to the public warning, or there was no plot at all.

The new system may be about as good an arrangement as we are likely to get if there is to be any warning system at all. The system probably is not quite as vulnerable to criticism as the stoplight chart. But with the passage of time, there will be renewed dissatisfaction. The public will complain about the lack of specificity in the warnings. The public also will complain about a lack of clarity regarding what the public is supposed to do in response to the warnings. With each alert that is not followed by an actual attack, there will be skepticism and bemusement regarding what the fuss was about. And when there is an attack, no amount of warning will prevent the inevitable recriminations.