It used to be that Saddam was supposed to show us his WMD.
Then it was: We had to find the WMD.
Then it was: He had to use the WMD.
Then it was: We had to suffer casualties caused by WMD used by Saddam.
I'm pretty sure that if US soldier die in a VX attack, the spin will be that the use of VX was justified, because we invaded their country.