Assad (allegedly) used WMDs (chemical weapons) in Syria, and that's a crime against humanity, so Obama is going to use WMDs (cruise missiles, bombs) in Syria too. That will show Syria how wrong it is to use WMDs. I mean, how wrong it is for them to use WMDs.
I'm trying to figure out how this makes sense, but I'm not sure I see it. But what would make sense to me would be for an international coalition to go into Syria and destroy and/or remove the chemical weapons, and then leave the combatants to fight it out without them.
