(NOTE: Despite the name similarities, this is not a spin-off of the early atom bomb thread)
Now, I know this scenario is implausible, but just play along. What if al-Qaeda had managed to pull of the hijackings and destruction caused in OTL almost the same as in OTL, but on September 11, 2000. First, how would the Clinton administration react? How would this affect the presidential race? What else would end up differently?