Not only is the battle for Aleppo sending tens of thousands of desperate people fleeing toward Turkey, but the fall of the rebel-held city would deliver a major blow to Ankara's Syria policy.
Syrian government forces, backed by Russian air power, have cut off the last major supply route to rebels in Aleppo. The route, known as the Azaz corridor, links rebel-held eastern Aleppo with Turkey.
If the corridor falls, the rebels could lose Aleppo -- and the entire Turkey-Syria border could fall under the control of forces that Ankara hates: the forces of President Bashar al-Assad's Russian-backed regime, and the Kurds.