The only way that it can be said the attacks only occurred after clinton left office is to ignore the first WTC bombing, the African embassy bombings, the Khobar Towers attack and the USS Cole attack. The 9/11 attacks were the culmination of a decade of previous attacks that weren't responded to.
BTW, I've read reports that the intent in the first WTC bombing was to topple one tower into the other. Had that plan been successful, both towers would have been taken out in a matter of minutes, allowing no time for any evacuation to take place. The death toll would have dwarfed the losses on 9/11.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Yes, the Towers would have collapsed in a sideways manner, taking down other buildings in their path. The death toll would have been enormous.
In 9/11, the buildings essentially imploded, and therefore, did not do as much damage to the surrounding building.
I think I added another post that is relevant.