Paris: Would establishing that Syria has used chemical weapons be enough trigger international intervention?

Yes, if the Responsibility to Protect still means anything at all. Establishing the facts of WMD will be critical this time around, and there would need to be major international agreement. A coalition of the willing? If any of this looks improbable, for reasons that have been rehashed ad infinitum, the international community will be seen to be utterly helpless. At the very least, proof of chemical weapons’ use should trigger a Security Council referral of President Bashar al-Assad to the International Criminal Court for crimes against humanity.