Weapons of Mass Destruction include Nuclear, Biological and Chemical, so yes, Sarin is a WMD.
George W Bush: Iraq Had No WMDs
https://m.youtube.com/watch?v=soohikNdbWs
We’ve heard morons claim sarin isn’t a WMD before. http://www.freerepublic.com/focus/news/1137857/posts?page=277#277