Secretary of State John Kerry has issued an ultimatum to his Russian counterpart: Either Russia stops the bombing of Aleppo by Russian and Syrian forces or the U.S. will end its cooperation with Russia in the region. Even the Associated Press sounds skeptical about what this will achieve:

Kerry’s warning came in a telephone call Wednesday to Russian Foreign Minister Sergey Lavrov, the State Department said, describing the latest U.S. ultimatum in Syria’s 5½-year conflict. Many have gone unfulfilled, including President Barack Obama’s declaration that the U.S. would take military action if Syrian President Bashar Assad crossed the “red line” of using chemical weapons.

It was unclear what effect Kerry’s words would have.

“The burden remains on Russia to stop this assault and allow humanitarian access to Aleppo and other areas in need,” Kerry told Lavrov, according to State Department spokesman John Kirby.

Kerry said the U.S. is preparing to “suspend U.S.-Russia bilateral engagement on Syria,” including talks on a possible counter-extremist partnership, “unless Russia takes immediate steps to end the assault on Aleppo and restore” a cease-fire.

I’m not sure what this is going to accomplish. The Obama administration is clearly frustrated that a cease-fire agreement which Kerry spent months negotiating fell apart in less than a week. It collapsed when Russia bombed a marked UN aid convoy delivering food and medicine to Aleppo. The Russian explanation—actually, there were several but the one they settled on—was that the convoy was destroyed by a cargo fire. That’s adding insult to injury.

The U.S. response is to condemn Russian “barbarism” in Syria at the UN and warn that this could be considered a war crime. But the underlying assumption here is that Russia wants the conflict to end and cooperation with the U.S. is the way out. What if it doesn’t want the conflict to end? From the Washington Post last week:

At a news conference in New York, [Russian Foreign Minister Sergey] Lavrov offered a starkly different point of view. He said it is the United States that needs to come around to the idea that President Bashar al-Assad is the only viable partner in the fight against terrorism, calling his army “the single most efficient force fighting terror in Syria.”

“Little by little, life will make everyone understand that it’s only together that you can fight terrorism,” Lavrov said.

His comments, alongside the events of the past week, suggest that Russia and Syria still believe the war can be won outright, without recourse to negotiations that the United States has said offer the only way out of the Syrian tragedy.

In short, maybe the Russians want to press the advantage and try to win this war while Kerry keeps talking about a cease-fire that gives a reprieve to Assad’s enemies. If so, how is Kerry’s ultimatum supposed to work? Kerry is threatening to take his ball and go home, but Russia has already made clear it’s not interested in playing his game.