Why is President Obama playing into the Russians' hand?

The Russians have wanted a warm water port in the Mediterranian area for as long as they have had a navy. They have a small one in Syria. They do not want to lose it, nor do they want to risk getting into a fight with the US in Syria. They would simply love it if the US would leave their buddy Assad alone and go fuck up someplace else.
So they offered to broker a deal whereby Assad gives up his chemical weapons (purchased from Russia), he can continue to kill Syrians with machine guns, helicopters and bombs, the Russians come back to their base, and the President retreats with only a little bit of egg on his face.
How is that a good deal?