imagine if on September 10th, 2001, President George W. Bush, citing increased "chatter" about an attack on the United States decided to shut down all airports nationwide. Furthermore, in an address to the nation he announces that Osama Bin Laden is behind the threats and has decided to invade Afghanistan and overthrow the Taliban. Can you imagine the response?
That would have prevented 9/11 (although it might have become 10/11 or 10/21, or some other date). However, I think the response would have been a very strong belief that George W. Bush had gone insane and was power mad. Further, there would be many calls for impeachment/removal on the grounds of mental instability or some such.