Via the Free Beacon, not only does chlorine have a long history as a chemical weapon, it was the very first chemical weapon used on the western front in World War I, by the Germans at Ypres. The key word here, though, is “listed.” Chlorine isn’t listed as a weapon by the OPCW for the simple reason that it’s used ubiquitously to decontaminate water. If you try to reduce access to it, you risk cholera epidemics in poorer countries. Problem is, as the Germans discovered, undiluted chlorine gas also works reasonably well as a crude WMD. It’s a weak agent compared to sarin or VX so it’s more likely to sicken the targets than to kill lots of them (although a few fatalities aren’t uncommon), but it works. Even O acknowledges here that it can be used as a weapon.

So why’d he feel obliged to footnote his answer by mentioning how it’s categorized under arms control protocols? It has to do with “red lines.” His escape hatch from the “red line” fiasco two years ago, you may remember, was to cancel a U.S. attack on Assad and make a deal with Putin to have the regime in Damascus hand over its chemical weapons. A lot of WMD was liquidated in the process; whether all of it was remains unclear. Just because Assad’s divested himself of some sarin and VX, though, doesn’t mean he’s going to respect Obama’s “red line” against gassing civilians. The solution is chlorine, a supply of which the regime maintains ostensibly for water purification but which will do in a pinch if you want to try to kill defenseless people, especially children:

On March 6, 2015, the UN Security Council condemned the use of chlorine as a chemical weapon, though at Russia’s insistence the council didn’t name the Syrian government as the perpetrator or impose any sanctions.

And yet ten days later, I watched videos sent by my Syrian colleagues showing dying and newly dead children, unbearably vulnerable to the chlorine dropped on them. After the first chlorine bomb went off at 8:30 PM, one entire family—three very young children, their parents, and their grandmother—took cover in a basement, knowing there would likely be a second bomb. The lights literally have gone out in most of Syria, so it was pitch-black in Sarmin, a village in the northwestern governorate of Idlib, where the attack occurred. No one could see the yellow gas, but they could smell it. The second bomb struck their house, trapping them inside, where they would suffer increasing difficulty breathing and ultimately suffocate to death. Dr. Muhammad Tennari described the chaos:

“The children came in their sleeping suits. The grandmother was dead on arrival but there was nowhere for her body. We had to place two of the children on top of her body, trying to resuscitate them…. We barely had water to wash patients, let alone oxygen or life-saving ventilators. No clothes for the children, left naked. And other casualties kept on coming.”

The reason Obama’s keen to emphasize how chlorine is “listed” is so that Americans won’t scratch their heads over why gas bombs are still dropping, having heard for months from the White House about how we supposedly convinced Assad to give up his WMD. It’s a way to suggest that the “red line,” which never should have been raised by O since he never really intended to enforce militarily, is being respected even as Syrian kids are choking to death on chlorine. And of course, even if the UN or OPCW confirms that chlorine was used recently in Syria, the fact that it’s not prohibited under international law is a way for O to justify not acting militarily against Assad later. Using a substance that’s not formally banned presumably requires a lesser response than an attack — maybe sanctions, maybe something else. Or maybe nothing at all, given that Assad and his Iranian sugar daddies are the last, best hope of keeping Syria from falling to ISIS.