I have generally supported current US policy in many parts of the Middle East, but in Syria the problem is discerning what that policy is. We're against ISIS. We're against Asad, though he's also against ISIS. We like the Free Syrian Army but not Jabhat al-Nusra, though they support each other. We generally like the Syrian Kurds but our NATO ally Turkey doesn't, Some of them are coordinating tactics against ISIS with Asad; others are fighting him. I'm oversimplifying, of course. But we are seeing several layers of progress by regime and regime-allied forces. Rebel supply lines north to Turkey have been cut, and the pincers are closing around Aleppo. Some pro-Russian, pro-Asad reports suggest only a few hundred meters may remain before the pincers lose. Even if that is an exaggeration, it is clear that Aleppo will soon be surrounded. A city already largely under siege of years is soon to be cut off entirely. Besides the closing pincers around Aleppo itself, all of Idlib province is also largely cut off from most supplies, including food.
It's said that in Aleppo itself 300,000 people could find themselves trapped with no means of exit.
In military history, one of the goals of strategic planners has always been to achieve a double envelopment of the enemy in which he has no means of escape. From Cannae to Stalingrad, it has been a means to decisive victory, but when a major city is surrounded and besieged, it is not just enemy soldiers but innocent civilians who will be destroyed.
The German theorists of war called the battle that results from a double envelopment a Kesselschlacht, a "cauldron battle" in which the surrounded forces (and civilians) have no outlet. And that's what appears to be coming.