I'm not sure if you remember this far back, but after the Iran Hostage Crisis, the U.S. was looking to topple Iran and helped arm the Iraqis any way they (well, really we) could. It was the U.S. that helped Iraq obtain the mustard gas, which they did initially use in the Iran/Iraq war, but of course, you can't trust Saddam. He was a U.S. asset until he wasn't want, probably sometime around the time he invaded Kuwait. I've read some evidence that suggested the U.S. even gave him the greenlight for the invasion, then pretended like we didn't. Who knows?

During the lead up to the Bush II invasion, you might remember the whole Anthrax scare, which was total bunk regarding it's connection to the Iraqis. Remember, they pushed the mobile labs and drones (before drones were even a thing) flying to America and killing us all. I believe Rumsfeld had stock in the Anthrax antidote and people rushed to Home Depot to buy tarps and masking tape to "protect" their houses from Iraqi death drones that never, could ever, possibly happen back in then.

What I read was that Saddam had tried to build some kind of massive cannon, but couldn't finish it. He was on the U.S.'s shitlist, so you would have to be out of your mind to sell him nukes. So when you're talking about WMD's, you're not talking about Mustard Gas. By that point, it wasn't even on the radar. Even if the Iraqis had somehow saved a stockpile, it would be unlikely that they'd ever have the capacity to deliver enough of it into a populated area.

WMD's were about nukes, Anthrax and maybe more advanced Scuds from the previous war, but since one was fiction and the other two were probably supplied by us--- I'm pretty sure the Intelligence Community knew Saddam's only chance was hoping no U.S. president would be crazy enough to spend the money to depose him, since he was keeping a lid on the ethnic/religious tensions there. I also read that Saddam was looking into creating his own currency exchange so that the Russians and other countries could use something other than American dollars to buy oil--- Something the Saudis and the U.S. Admins would not tolerate.