Listen, to you and me, to normal people, WTC was enough of a wake up call. Many of us were already awake, but putting that aside, WTC should have been the straw that broke the camels back, so to speak.
Yet, i think there are people (millions) who will not wake up until lets say 2 nukes go off, maybe one in tel-aviv and one in new york, london, paris (would that be so bad?, j/k)take your pick...
2 nukes? You know, I think you're right.
All the worry about airplanes, buildings etc is nonsense and old news. OBL and Al Qaeda always try something new.
I fear the nuclear or bomb with radioactives is the most potent threat. It even has Biblical implications. The most likely targets are Tel Aviv (the most Jewish and least Arab-objectionable site in Israel to bomb) and either NY or Washington, DC ("to destroy the head of the snake").
What is truly terrifying is that these types of attacks are not only possible, but very likely as the world moves further into widespread proliferation of nuclear materials and knowledge.
The timer for our nation is ticking.