The biggest mistake was that a crime was treated as an act of war. When civilians attack civilians, that's crime, not war. We have efficient police agencies to deal successfully with crime, to seek out and apprehend the miscreants and bring them to trial. But Bush reacted to 9/11 by calling it "war" and appointing himself a "wartime president" with all kinds of new powers to control the American people. Last time I read the Constitution it was up to Congress, not the president, to declare war.
The next major mistake was invading Iraq. The attackers of 9/11 were not Iraqis; they were Saudi Arabians. If Osama Bin Laden is responsible for 9/11, as he claims but which cannot be considered proven until there is a trial, then why not go after Osama as a criminal? He seems to be safely in Pakistan.
If there is indeed evidence for Osama's responsibility, as he claims, then it is a disgrace that he is still at large while vast expense and effort is dedicated to beating up on Iraq as if Iraq had attacked us which it never did.
Osama Bin Laden is Saudi Arabian, and the Bush family once had extensive business dealings with the Bin Laden family. Is Bush now protecting Osama Bin Laden and going after Iraq as a distraction? Why is Bush pussyfooting around the fact that Osama is in Pakistan, not Iraq, and that Pakistan is ruled by a dictatorship, not a democracy? If building democracy in the region is a worthy goal, why do it in Iraq instead of Pakistan?
The Constitution of the United States