It's not quite the same thing.  In 2004, GW Bush lost confidence in the CIA precisely because they told him that Hussein had nuclear and biological WMD.  It wasn't mustard gas that they said.

Bush actually was so disappointed with his intelligence service that he says "they don't really know what's going on" --- approximately, since Bush in the history books is saddled with this disaster of claiming WMD and invading iraq just because Hussein was bluffing about having nukes and the CIA believed that.   Didn't matter, the buck stops at Bush because it was his call.  GW Bush to his credit didn't shift the blame onto the CIA or to Cheney, he was still responsible for that giant mistake.

Chemical weapons are not quite at the same level as nukes.