It's time for the United States to hold Iran accountable.

Secretary of State John Kerry was not invited. Nor was the United Nations consulted.

With pro-government forces having made critical gains on the ground, the new alignment and the absence of any Western powers at the table all but guarantee that President Bashar al-Assad will continue to rule Syria under any resulting agreement, despite President Obama’s declaration more than five years ago that Mr. Assad had lost legitimacy and had to be removed.

Mr. Obama’s reluctance to back that demand with more involvement as the war escalated leaves Washington with little leverage on a geopolitical crisis as President-elect Donald J. Trump prepares to take office.

Mr. Trump’s only recent statement on Syria came last week, when he declared at a Pennsylvania rally that the situation was “so sad” and promised, “We’re going to help people.” He vowed to extract funds from Persian Gulf nations to build “safe zones” in Syria “so people will have a chance,” without addressing the question of who would enforce those zones on the ground or in the air.

But by the time Mr. Trump is sworn in next month, such safe zones may be irrelevant, if the evacuation of Aleppo and political negotiations proceed.

More than a year after launching the air campaign that remade the battlefield in Mr. Assad’s favor, Russia appears to be looking for a way out of the war. Analysts say that Moscow sees in the transition an opportunity to end the conflict on favorable terms both for Mr. Assad and for Russia’s broader interests in the region.

“Russia understands that nobody gives you anything, you just have to take it, and in this environment, with the U.S. retreating faster than the other side can advance, it’s just a free for all,” said Andrew J. Tabler, a fellow at the Washington Institute for Near East Policy who studies Syria. “When the Turks, the Iranians and the Russians all agree on a process without the U.S. being in the room, you realize there is a problem for us.”

Russian officials have made little effort to hide their disdain for American diplomatic efforts.

Last week, Foreign Minister Sergey V. Lavrov said working directly with Turkey on the evacuation deal was more efficient than “fruitless get-togethers with the U.S.” On Tuesday, Mr. Lavrov said the International Syria Support Group, which he and Mr. Kerry led since 2015, had turned out “important documents,” but “has been unable to play its due important role in seeing to it that adopted decisions are implemented.”

Click here to read more.