The answer, according to Kaplan, is that confiscation of Assad's chemical weapons is in the best interest of Russia:
Putin must have seen this distinction as confusing at best, duplicitous at worst. War, after all, is by nature political; military strikes always have political objectives. This is why he had so firmly opposed any talk of punishing Assad for using chemical weapons: He figured that U.S. airstrikes in Syria would be a pretense or prelude to deeper intervention and “regime change.”
However, when Kerry said that dismantling the weapons might halt the juggernaut of U.S. military action, Putin saw an opening. He took the narrowest slice of Obama’s rhetoric literally: that the coming airstrikes were strictly about Assad’s chemical weapons. OK, then, Putin replied: I’ll help to remove those chemical weapons, and you call off the airstrikes. End of story.
And so, assuming all goes according to plan, Assad loses his stash of deadly chemicals—but he stays in power, at least for the time being, and the Russian Federation re-emerges as a serious player in Middle Eastern politics. A win-win-win for Putin.
I'm hoping, of course, that Kaplan is right, but I think there's a better than halfway chance he is right if only for this piece of reasoning he offers later in the piece: that is Putin had other designs than the actual removal of Syrian chemical weapons, there was no reason for him to act before the vote in Congress that Obama looked sure to lose. Putin could have waited for Obama to get embarrassed, and then offered a half-hearted gesture toward diplomacy to make Russia look a bit better on the world stage, a gesture that would almost certainly have led to no real action. The likeliest reason to make this international deal now is that they want to get it done.
It brings to mind the words of John F. Kennedy in his speech at American University in June, 1963:
We are both caught up in a vicious and dangerous cycle, with suspicion on one side breeding suspicion on the other, and new weapons begetting counter-weapons. In short, both the United States and its allies, and the Soviet Union and its allies, have a mutually deep interest in a just and genuine peace and in halting the arms race. Agreements to this end are in the interests of the Soviet Union as well as ours. And even the most hostile nations can be relied upon to accept and keep those treaty obligations, and only those treaty obligations, which are in their own interest.The biggest variable now is not Russia, but Assad himself. What will he do, now that his great benefactor Russia has struck this deal with his great enemy, the United States?