Big jump
The manner of the surprise Russian intervention clearly shocked Washington and its allies, and set back any prospect of productive settlement talks for the moment.
But it's worth remembering that the two sides have some shared strategic objectives.
Both want to contain, and preferably altogether destroy, the militants of IS.
Neither wants a regime collapse and rebel victory that would inevitably mean Islamic militants taking over Damascus, even if the flags had different shades of black.
But it's a big jump from that to agreement on a diplomatic way forward out of the daily bloodbath.
And at the core of the knot, as ever, is the future of Bashar al-Assad - not just his own person, but everything he stands for, and what kind of Syria his departure would make way for.