Let's play You Are the President.
There are reports that Syria has used chemical weapons — sarin gas, to be specific — against its own citizens. Rebels claim they were attacked by a Scud missile that released the gas. Reports indicate between 15 and 40 deaths, and there seem to be third-party confirmations. The Syrian government says that it was the rebels who carried out the attack, not the government. But, it is also public knowledge that the Syrian government restarted its chemical weapons program some time ago, and it seems logical that the government fired on the rebels and not the other way around.
Iran condemns the attack. Russia seems to stand with the Syrian government. All of Syria's neighbors, including Israel, are nervous that this attack means Syria has both the means and the will to use chemical weapons against other countries.
And yet, there are questions. Why such low numbers? Typically, if you release gas in a battlefield situation, you want to kill or injure many more than a few dozen. Could this have been an accident? Could someone have fired a missile they thought was conventionally armed, only to see it release gas? And, even if this was intentional, does it indicate that Syria doesn't have a well-formed delivery capability, and isn't really a threat if it has to rely on Scud missiles to deliver the gas?
So, if You Are the President, what do you do?