PETN, in other words, isn’t a weapon of mass destruction. It can take down a plane, but not a city. It requires “a fair amount of training and experience” to deploy, but not advanced degrees in chemistry or physics. It is far from fail-safe. Which is exactly my point: If al-Qaeda terrorists are stuffing PETN into underwear or packages, that must mean that they do not have access to cutting-edge biological research or nuclear bomb components. On the contrary, they remain strangely fixated on airplanes and far behind the technological times.

Clearly, this latest incarnation of al-Qaeda is not benign: Islamic fundamentalist terrorism remains a threat, and the terrorists responsible for this latest attempt appear to be looking for weaknesses in the international aviation system. One day they may succeed. Yet although they are dangerous, although they are ruthless, these package bombs prove that al-Qaeda, at least in its desert hideouts on the Arabian Peninsula, does not pose a serious, existential security challenge to the United States.