The Obama Administration clearly decided years ago that the only possible way of reaching an outcome that would be reasonably consistent with our interests and values (i.e., no sectarian massacres, ongoing militia battles, or American ground war and occupation) would be through a negotiated settlement. As a result, our policy, which in reality has been quite consistent, has looked indecisive and unheroic. I believe there have been three stages to this approach:
1. Make a deal with the Russians: In the early stages of the conflict, it seemed possible to ease Assad out of power by persuading the Russians to find a more acceptable surrogate. Unfortunately, the Russians, for a variety of good and not-so-good reasons, would not go along with this, and the regime did not fall, which led to:
2. Hope that a stalemate would result, and the parties would be driven to make a deal: A stalemate of sorts did occur, but this stage was dominated by the unforeseen rise of IS, which clearly could not be a party to any kind of negotiated settlement. So here is where we are:
3. Focus on IS, and keep your options open: The ideal solution would be the replacement of Assad by a much cleaner member of his regime, some degree of nonsectarian democratic reform, and a broad alliance of the remaining elements of the regime and the more moderate rebel groups against IS. If that proves to be impossible, strangle IS (the greater danger to US interests) and then deal with the regime. Russian and Iranian cooperation is almost certainly necessary to make the preferred scenario realistic.
The connection between #3 and the Iranian nuclear deal is obvious. It would appear that the Russians are starting to show some flexibility, as well. We will see.