There is the smell of a kill in Syria, where expectations are high in some quarters that both President Bashar Al-Assad's regime and the Iran-Syrian-Hezbollah axis may soon break. 

That outcome may be far from assured. Much hinges on the battle of Aleppo, which Assad’s forces could win. If this happens, the regime would have its second wind, even as it loses territory elsewhere in the country.The opposition would be set back.  Assad will keep up the fight even if weakened and diminished, especially as long as he has the support of Tehran and Moscow. The bloodshed could go on for months, or longer.

The best option for the US could be a revived diplomatic track, this time involving Iran, which might have the best chance of ending the violence.

Iran is not giving up the fight and has shown its own diplomatic heft. Tehran hosted a ministerial-level conference on Syria last week attended by representatives from more than two dozen countries, including Russia, China, Iraq and Jordan, as well as the United Nations. The final statement called for negotiated solution to the crisis in Syria.