But as with the viral pandemic we are now facing, the challenge with this terrorist alert system was not the difficulty in concluding that there was a specific and credible threat. Rather, it was in answering the opposite question — when has the threat sufficiently receded so that we can drop from red alert to a less restrictive security regime? That decision was very difficult, because a premature all-clear could result in dropping guard against a still imminent threat, with horrific results. Intelligence and security professionals, and political leaders, still smarting from the failure to avert 9/11, were under considerable pressure to maintain maximal protection, lest they be blamed for a subsequent terror incident. But there are considerable economic and social costs to this.

That dynamic is reflected in the current debate about pandemic restrictions. If the only imperative is to eliminate risk of serious illness or death, then a long-term blinking red alert with the most restrictive social and travel restraints, is an obvious recourse. Indeed, we see this with increasingly draconian interstate travel bans being ordered by some governors. But the economic and psychological consequences of unrelenting security measures can be high, and debilitating over time. While total risk-elimination may seem the proper objective for security professionals, the collateral damage may be very substantial and even irreversible. Imagine the results if, after the discovery of the 2006 airline plot, we had grounded passenger aircraft for an extended period of time, instead of simply imposing limits on carry-on liquids.