Terrorism aims to undermine government by demonstating that it can't protect its citizens, in theory the poplulation then become so disatisfied that they turn on their leaders and create a situation ripe for radical change. I don't know that it has ever worked in reality, it seems more like desperation born of impotence. In any case it's not hard to understand how necessary it was to roll out all available resources, especially since it was going to come out that the FBI dropped the ball again.