The National Security Archive “posted some declassified documents”:http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB358a/index.htm on Sept 11. Most of them have nothing to do with WMD, but there are a couple of exceptions.
“This one”:http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB358a/doc13.pdf is a 9/30/01 memo for the President from then-SecDef Rumsfeld. The memo is about the aims of U.S. military action post- the 2001 attacks. Right near the end, it states
bq. The regimes of such [terrorist-supporting] States should see that it will be fatal to host terrorists who attack the U.S. as was done on September 11. If the war does not significantly change the world’s political map, the U.S. will not achieve its aim. There is value in being clear on the order of magnitude of the necessary change.
The memo goes on to list some goals that the United States should “envision,” one of them being “dismantlement or destruction of WMD capabilities in [redacted] and [redacted].” Everyone can fill in their own blanks, I suppose.