"I would assume, though, that the explosive is imported, manufactured somewhere else. That stuff is widely available on the world scene in two, five and ten ton lots. You'd have to import the precursors to make the good stuff, anyway, may as well just import the explosive."

The HE of terrorist choice by the belt bombers, as I understand, is TATP (Tri acetone Tri peroxide). This requires 3 ingredients that you can get from a trip to a beauty salon and a hardware store... It is a plasticized version of this that the shoe bomber tried to use on his flight. The truth is terrorists dont need to import any explosives... A wannabe belt bomber with a few hundred bucks could do it here... Should we close all hardware stores and beauty salons? No, but we need to realize that there is little defense against a suicide bomber except to find him before he enters the US.
BTW as a side note- another student visa was approved recently for one of the now dead 9/11 terrorists...:) Really makes you feel confident doesnt it?