This is pretty out there, from the excellent Julian Borger of The Guardian:
On 19 March, both the Assad regime and the rebels claimed nerve gas had been used against their forces at Khan al-Assal. British officials say Syrian army troops appear to have been affected in that incident but suggest it was either a case of "friendly fire", a projectile going astray, or a deliberate attempt to implicate the rebels.
A deliberate attempt to implicate the rebels? So they sarined some of their own people to set up the FSA? Wow. That is hard core. Like a Bond villian. Or like Gene Tierney in Leave Her to Heaven. If you haven't seen that and don't know what I'm talking about, you should. It's a pretty great movie, and anyway even a bad movie is good if it has Gene Tierney.
Now, being more serious, this is a really frightening situation. I was profoundly concerned when Obama made those remarks about a "red line" months ago, for the obvious reason that we knew this day was going to come. What has he locked us into?
There exist many options right now short of intervention. This will hinge to some extent on how things go with Russia. The first move is to try to get Russia involved in some kind of sanction through the Security Council.
This is a terrifying situation. On the one hand, chemical weapons occupy a special place in warfare hell going back to the 1920s. The world's civilized nations have long agreed that chemical weapons are uniquely evil, good at killing huge numbers of civilians but with little real battlefield value, which is why they are uniquely proscribed. So when someone uses them, the world has to do...something.
On the other hand, we just can't have another war. That way sits disaster. Obama surely knows this. But we've seen leaders get sucked into things before. Go back and read about how World War I started. Willy and Nicky thought they had the whole thing under control. Yikes.