Huh? Obama tried to stay clear of Syria. The damage was done by US in a round about way, the second Iraqi war and it's aftermath which left a huge power vaccum in the region, and killing many US troops and Iraqi and Afghani civilians. Which is exactly why Obama didn't want to get the US stuck in there.
Russia and Iran stepped in to enlarge their hegemony, and they put the Assad regime back in power.
So kindly blame Russia and Iran for this.