You know it was coming (honestly, I was surprised that a thread hadn't already been posted). What if September 11th, 2001 had been just another perfectly ordinary and uninteresting day, with no hijacked planes, destroyed skyscrapers, national calls for vengeance, or the like? Certainly no 20th anniversary remembrances? Presumably, for this to happen the terrorists would have to have been caught before they could board the planes and begin the attacks. The most straightforward way for this to happen would probably be for intelligence sharing to be slightly better, so that the FBI realizes what is going on and is able to arrest at least some of the plotters before they attack, enough to either capture the whole group of hijackers or enough that they can't successfully carry out the attack. But what happens next?