The safeguards that are employed in airport security policy are found using the “best response dynamic”: Each player chooses  the optimal response to their opponent’s strategy from the last period.  So, the T.S.A. best-responds to the shoe bomber Richard Reid and a terrorist plot to blow up planes with liquid explosives.  We end up taking our shoes off and having tiny tubes of toothpaste in Ziplock bags.  So, a terrorist best-responds by having a small device divided into constituent parts and hidden in his underwear.  One part has to be injected into another via a syringe and the complications that ensue prevent the successful detonation of the bomb.  In this sense, each player is best-responding to the other and the airport security policy, by making it a bit harder to carry on a complete bomb, succeeded with a huge dose of good luck thrown in.

What should we learn from the newest attempt to blow up an airplane?

First and most obviously, the best way to minimize the impact of terrorism is to stop terrorists before they can even get close to us.  This appears to be the main failure of security policy in the recent incident – more focus on intelligence and filtering of watch lists is vital.  Second, the best response dynamic should not be the only way to inform policy.  There are already rumors that no-one will be allowed to walk around for the last hour of the flight or have personal items on their lap.  Terrorists will respond to these policies by blowing up planes earlier in flight.  Does that make anyone feel any safer or the terrorists less successful?  The main problem is that terrorists are thinking up new schemes to get to nuclear power stations, kidnap Americans abroad and other horrible things that should being brainstormed and pre-empted.  The best response dynamic is backward looking and cannot forecast these problems or their solutions.  This second point is also obvious.  The fact that a boy whose father turned him in got on a plane with a bomb suggests that even obvious points are worth making.