Obama's main mistake in Syria was drawing the Chemical "red line" to begin with. The war there is no more horrible this week than it was last week, regardless of the weapons used. There are several groups of psychopaths fighting each other, and fighting to support one of them will not make things better. It would only serve America's need to "do something" and generate business for the world's military industries.
What the West should do is set up safe areas along/near Syria's borders where civilians can relocate and be provided for. It would save more lives, cost less, and will not bring about a worst outcome in a situation where all options are bad anyway. It would also carry more moral weight and be more principled than forcing the hand of yet another country and then leaving it in an even bigger mess (Afghanistan, Iraq, Lybia, Egypt, etc.).