Just to show I'm not blowing smoke (as it were) about mustard gas, here is an excerpt of a document on Iraq and Iran's WMDs prepared in 1998 by the Washington Institute for a body called "The Rumsfeld Commission," which I assume was headed by Rumsfeld:

Chemical Weapons Iraq is believed to still possess a small stockpile of lethal agents, munitions, precursor chemicals, and production equipment that provide it with the ability to inflict massive casualties on an unprotected civilian population, though it probably does not have sufficient quantities of chemical munitions for effective battlefield use. This residual inventory probably includes stocks of blister and nerve agents, possibly including quantities of "VX salt" -- a form of the highly lethal nerve agent that can be stored on a long-term basis. The U.S. government believes that if inspections and monitoring were to cease, Iraq could resume production of mustard agent in weeks, sarin within months, and VX in 2-3 years.iv

Note that Mustard Agent is included as a WMD in this report, along with other toxins.

Bobert, if you search on "Iraq WMDs" in google, you'll find gov't and think-tank reports that will give you a sense what's being talked about.