The gravest charge against George W. Bush is that he took the Coalition into war with Iraq in 2003, fully knowing Iraq had disposed of all it's WMD. However, now that volumes of captured documents from Iraq are becoming translated, it's clear that Saddam wanted to maintain to his own military, neighbouring countries, Iraq itself and the USA the belief that he had WMD until as late as December 2002.
An excellent article in the Christian Science Monitor reveals Saddam thought that the WMD he did possess in the 1991 Gulf War were the only things that kept the Coalition from toppling him then - and these would do so again in Gulf War II. He also needed to instill fear into the rebellious Shiites and Kurds he had previously gassed and terrorized, keep Iran guessing and maintain morale amongst his generals.
Saddam sent allies such as the Yemenis in 2002 to inform Dick Cheney that Iraq would retaliate with WMD if attacked, reinforcing belief that he possessed them. Vice President Tariq Aziz stated his generals were "stunned" and lost morale when he informed them in December 2002 that he actually had none and was bluffing. George Bush was not.
These documents of the innermost workings of Saddam's regime show that Bush made an error, but that he was right in saying every major intelligence agency in the world thought Saddam still had WMD and there was no reason to believe otherwise. Saddam wanted it that way.