Not that I would ever defend George W Bush, but a soldier just back from the Iraqi war at the time told me his unit was attacked with mustard gas.
I mean, honestly, so what?
Stipulate that Saddam Hussein's army had mustard gas, or sarin. Stipulate that they had mobile germ warfare labs. OK, go all the way and stipulate that they had guys in a bunker somewhere playing with U-235.
THAT DID NOT MEAN WE SHOULD REFIGHT THE VIETNAM WAR IN SOUTH ASIA.
The existence, or non-existence, of "WMDs in Iraq" does not excuse the failure to plan for war and occupation, even if you grant (which I do not) that Iraq as such had any strategic value in the war against the Wahabi/Deobandist Islam which attacked us on 9/11/01.
The main enemy remains, and sleeps securely in his beds in Riyadh and Islamabad.