The United States has two national security interests in punishing Syrian President Bashar Assad’s use of chemical weapons. First, it wants to deter the global use of weapons of mass destruction. Second, it wants to ensure the credibility of America’s word.

That matters anew in light of Secretary of State Mike Pompeo’s announcement on Thursday that the U.S. has concluded Assad again used chemical weapons in an attack in May. As in 2018 and 2017, the U.S. must again respond militarily. To do otherwise would be to invite the global conclusion that America’s word is meaningless.