After a few days of attacks by the Russians in Syria we can conclude that IS is not really the target. Instead it is mainly the US backed moderate groups and Jaish al-Fateh/Nusra who are targeted.
What could be Putin's plan.
We've heard a lot of motives for Putin to get into Syria: Draw attention away from Ukraine because that conflict is going nowhere, wanting a central position on the world stage, annoying the West and U.S. in particular, save his old ally Assad, save his mediterranean navy base, creating a negotiation position to keep the Crimea and/or get rid of the sanctions, strengthening his position in the Middle-East or even maybe become the Great Peacemaker.
All are probably true, or partially, or to a certain degree. What you want to do then is come up with a sort of endgame for Syria. The only viable endgame is a political solution where the regime (with or without Assad) negotiate a peace with the rebels (with or without Nusra)
Note that IS is not a party in these negotiations. They shouldn't be. For Putin they're not even that relevant as long as IS leaves the regime relatively alone, as they have done the last two years.
Putin wants to negotiate from a position of strength of course. When you start to talk to the rebels you want to do that from the position where the rebels feel they can't win militarily, when the regime is winning. Or at least the perception is that they're winning. Currently that's not the case.
But as we have seen momentum has changed sides several times in this war. First the rebels seemed to be winning, until the Iranians brought in Hezbollah. The tide seemed to be changing again when ISIS entered from Iraq in 2013 but they and the other rebels turned on each other. During 2014 it stayed relatively stable until the cooperation between Turkey, Qatar and Saudi-Arabia supporting the rebels started. The rebel coalition Jaish al-Fateh managed to make big gains this year in Idlib province which prompted the Iranians to ask Russia for help since Assad's forces are really short on manpower, Hezbollah had been severely battered, Iran doesn't really want to commit their own troops and Shia militias from Iraq and Afghanistan can't make the difference either.
It all comes down to get the timing right to start negotiations. Time is not on Putin's side. He cannot afford a prolonged war. Not financially and not at home. So if he can have a short offensive pummeling the rebels, getting rid of pockets like the one north of Homs and take back some parts of Idlib and the perception is they could go all the way to Aleppo and the Turkish border. Putin, at that point, might be 'convinced' by the West to have Assad negotiate with the rebels. Right now the rebels are in no way ready to talk to Assad but if you're losing you don't have much choice. That could result in a sort of deal for western Syria. The Caliphate will have to wait.
Then Putin is the great peacemaker, we forget about the Crimea, he may even quietly pull the plug on the rebels in Donbass, the sanctions are lifted and the West gets to continue the endless war on IS. Win-win for Putin.
But as the old Moltke adagium goes: No battle plan ever survives contact with the enemy. So a lot can go wrong along the way and it will be interesting to see how Putin will deal with the inevitable failures. Will he be sucked into the quagmire? Will he give up and leave or wil his intervention just peter out.
