But there were two important and deadly loopholes. The first was that Assad did not declare everything—a reality that Kerry acknowledged in a farewell memo to staff, in which he wrote that “unfortunately other undeclared chemical weapons continue to be used ruthlessly against the Syrian people.” The second was that chlorine gas, which has legitimate civilian uses, was not part of the deal. The Syrian American Medical Society and the White Helmets civil-defense group have documented 200 chemical attacks in Syria since 2012, many involving chlorine. On Saturday, the group alleged a particularly gruesome attack in the besieged city of Douma, which has reportedly killed dozens and injured hundreds. It remains unclear exactly what chemical weapon was involved in the alleged attack.

The deal’s failure to prevent attacks like this was evident even before last April, when sarin gas killed roughly 100 people in the Syrian town of Khan Sheikhoun. By then, Assad’s renewed campaign of chemical attacks, involving the use of chlorine in barrel bombs, was well underway. But sarin was explicitly prohibited, and those weapons were supposed to be out of the country. The deal, The Atlantic’s Jeffrey Goldberg wrote at the time, “was not a complete failure, in that [chemical-weapons] stockpiles were indeed removed, but Assad kept enough of these weapons to allow him to continue murdering civilians with sarin gas. The argument that Obama achieved comprehensive WMD disarmament without going to war is no longer, as they say in Washington, operative.”