Why should the Russians and Iranians make a deal if they have a winning hand? No diplomatic arrangement is possible. In fact, the diplomatic option is fictional. To put it flatly, there is no alternative.
It is not inconceivable that the White House would consider easing sanctions on the Iranian nuclear program to have a chance in Syria. What is likely then is stalling, with the probability that the civil war will settle into stagnation for several years and thus a de facto partition of Syria.
The United States simply can’t win given what it is willing to do. And in a great power standoff, that’s a very dangerous situation. Remember, though: Iran cannot be said to have won as long as the civil war is continuing. The administration can simply depend on denial, which should be sufficient for domestic purposes.
Finally, ask yourself one question: will the United States under Obama dare a confrontation with Iran, Syria, and Russia to keep up American credibility, deterrence, and the confidence of allies who it is already opposing on Egypt? Of course not.
This is a president who could barely decide to kill Osama bin Laden.