JP5 are talking about important things here. Remember that that an operation as huge and complicated as first acquire flight training, and then simultaneous hijacking of four airliners that it takes years in preparation. There is no way they would has canceled just because Al Gore had won the election, the attack would have been carried out regardless.

*Afghanistan would have been attacked anyway.
*Iraq would probably been ignored.
*America would have kept it's global support due to the lack of an Iraq war.
*Normally hostile middle east countries may have joined in on the "war on terror" and sought a better relation with the US. This may even have included Iraq. Al Quadia would because of this have a harder time to relocate it's operations.

The real difference are that I believe that the attack on Iraq was the result of an personal vendetta on president Bush's part.