Neither Afghanistan nor Iraq was a mistake.
Afghanistan was easily justifiable . . . we were taking out a government which, while not directly responsible for the 9/11 attacks on the United States, openly supported and provided safe harbor to those who were.
Iraq was not a mistake, because "mistake" implies that there was an "oops!" somewhere in the intelligence gathering and decision making process. I think that those in charge of gathering the information to provide GWB and company knew damn well that WMD and the supposed links to Al Queda were a stretch, at best. I also believe that GWB was sheltered from those details to provide him with plausible deniability (wink, wink) so that he could finish the job that his daddy was not allowed to finish.