The British foreign secretary, Philip Hammond, told me he had good reason to be skeptical of that optimism.

“There’s a school of thought that says that as the Russians get drawn into this conflict, they will more and more looking for a way to get a political solution,” he said — but “it’s not my government’s assessment.”

Hammond said he spoke with Russia’s foreign minister, Sergei Lavrov, the day before in Vienna after the talks concluded and Lavrov told him Russia did not have any flexibility on the issue of Assad’s departure. Hammond said that the Russian position on Assad is exactly the same as it was three years ago and that it’s likely to remain the same. Russia says Assad was elected, and only an election can replace him.

That would be “directly at odds with those of us who believe that Assad has so much blood on this hands that he has to depart before there can be a sustainable political solution in Syria,” Hammond said.