1 Provide security for Russian citizens in Syria
2 Bring in a few more weapons/ammo
3 Show the flag
Their presence does have some deterrent effect on western action I guess, but if chemical weapons get used I doubt the Russians would try to stop the west from responding. If they did it could get really ugly. I think Putin is as adventurous as he is diminutive but I also hope he's rational enough not to provoke a war over Syria. Having a tool like Obama in office makes this kind of equation dicey because he isn't respected. We do NOT need to be involved in Syria in any way. It's a no win for the US.