By all accounts, the two leaders remain distant and wary of each other. The Kremlin in particular has been frustrated by what it sees as Mr. Assad’s arrogance and, at least until recently, his unwillingness to bend to Russia’s wishes, on issues like jump-starting peace talks in Moscow this year and freeing dissidents who might play a role in any political solution.

“It’s not personal, this whole thing,” said Dmitri Trenin, the director of the Carnegie Moscow Center, referring to Mr. Putin’s intervention. The highest priority of the Russians, he said, has been saving the central authority of the Syrian state as much as Mr. Assad himself in hopes of stemming the spread of chaos and, with it, the fertile ground in which the Islamic State can take root.

“To them, Assad is not a sacred cow,” Mr. Trenin added. “The issue to them is to save the Syrian state, to prevent it from unraveling the way Libya unraveled, Yemen unraveled.”…

The question now is whether Mr. Putin can press Mr. Assad to accept a negotiated end to his rule. “Putin’s influence over Assad is like Obama’s over Netanyahu,” a diplomat based in Syria told a group of colleagues several months ago, before the Russian military intervention began, referring to the often truculent relationship between the American and Israeli leaders.