I don't know if they could have done much worse with more time, but I do wonder why we didn't go after them before 9/11 as well.
Especially when our government has had one of their members, Mousaaoui, a likely 20th member of the 9/11 conspirators group, in custody since August. But they never got warrants to search his home, etc., until after 9/11. Hindsight is 20/20, but that certainly turned out to be a grave mistake. He was taking flying lessons, getting $ sent to him, etc., that much we knew so we should have been more alert, and perhaps taking action abroad. We wouldn't have know about the planes in to buildings plot to specifically guard against that, but it should have sent up a red flag alert towards all aviation targets in general, and possibly prompting us to do something abroad. The warnings about cropdusting tactics is just one of the specific things that came about from the post 9/11 warrants served on his home and computer.