If I felt that Obama's actions would tilt the battle either way, I wouldn't support him. America and France don't need to own what happens to Syria which I feel will be a lot more bloodshed. Furthermore, letting a dictator kill civilians with banned weapons isn't something the international community should ignore.
All of these countries, and the US, have signed on to the chemical weapons ban treaty. And they have decided to be spectators, because "they don't have to get involved." Now it's time for the adults in the room to act like adults.