I'm just putting myself in his shoe. What would a mad man do? Suppose I do have a weapon of mass destruction. I can't use it on the U.S army because they're out of range. I can't target civilians because that's a terrorist act. I hate the U.S because they've been out to get me for the past decade. What be perfect is if an advancing U.S army went inside Iraq, I detonate the weapon within my own territory crippling the U.S ground force. True I'd be nuking parts of my own country, but I'm a madman so I don't care, and I don't mind killing my own people at all. The U.S can't cry about it because I didn't nuke one of their city with civilians inside. It was an attack that only took out a millitary target.
If they U.S attacks Iraq this time, how likely is it that something like this will happen? If we place tens of thousands of ground troops in Iraq, they might be walking right into a trap.