People have short memories, or perhaps, they just want to find any excuse they can to attack this president. We did not go into Iraq because they had WMDs. We went in there because Iraq repeatedly violated the 1991 cease-fire agreement and the U.N. Security Council was not willing to do anything about it except play the Hans Blix shell game. We had no idea if Iraq had WMDs or not. Yes, our thinking was that they had them. But how could we know for sure unless Iraq gave us complete and total access to the entire country?
Since the 1991 cease-fire (yes, we have technically been at war with Iraq since that time), the U.N. has passed over a dozen resolutions which Saddam repeatedly thumbed his nose at.
We know that Saddam had WMD's in the past and used them against his own people. This is why at great expense, we have maintained no-fly zones over north and south Iraq - so that Saddam could not commit mass-murder against his own people.
We also know that Saddam had a history of making unprovoked attacks against other countries (Iran, Kuwait, Israel). We'd be nuts to leave him in power after 9/11 and sit around waiting for him to attack a fourth (which might well have been us).