The Obama-Trump doctrine that the United States will enforce a global norm against the use of chemical weapons is strategically pointless and morally arbitrary. Strategically, it requires the United States to invest its time and resources policing a weapon this is not qualitatively different from conventional weapons. Morally, it amounts to a declaration that the United States cares more about the murder weapon than the murder victim.
Assad, for example, has killed hundreds of thousands of people, but we’re only supposed to get upset when he kills them with chemical weapons? The reasoning for opposing chemical weapons is that they can be deployed in an arbitrary fashion that kills a lot of innocent people and they result in a gruesome death. One could make the same case for the MOAB.