With Barack Obama's presidency coming to a close and US policy for Syria at an impasse, Vladimir Putin's Russia has stepped up efforts to secure its ally Bashar al-Assad in power.
US officials fear the Kremlin is racing to consolidate its gains in Syria before a new, possibly tougher administration takes charge, but there is little sign of a clear new policy emerging.
On Tuesday, Republican flag-bearer Donald Trump's vice-presidential running mate Mike Pence split from his candidate's admittedly vague position by calling for air strikes against Assad's forces.
"The small and bullying leader of Russia is now dictating terms to the United States," he complained. "I just have to tell you that the provocations by Russia need to be met with American strength."
And if Russia continues to support "this barbaric attack on civilians in Aleppo," he added, "the United States of America should be prepared to use force to strike military targets of the Assad regime."
Democratic challenger Hillary Clinton has also called for stronger action, suggesting the US military enforce a no-fly zone, but it is far from clear how one would work in practice.
For his part, Trump has sent confused signals, suggesting at one moment that Putin could be a friend of the United States and at another, that Obama was weak not to confront him.
"I don't love Putin, I don't hate. We'll see how it works. We'll see," Trump told supporters Wednesday in Nevada.
"Maybe we'll have a good relationship. Maybe we'll have a horrible relationship. Maybe we'll have a relationship right in the middle."
Fighting erupted in Syria more than five years ago, when Assad brutally suppressed a civilian uprising and triggered a civil war, creating a power vacuum that allowed jihadists to seize territory.
Confidently predicting that Assad would fall to his own people, Obama concentrated US action on building a coalition to fight one of the factions, the would-be global Islamic State (IS) jihadist group.
Assad clung on, however, and last year Putin sent warplanes and troops to back up his ally, ensuring a bloody conflict that has already killed 300,000 people will continue.
The refugee flows created by the war have threatened to overwhelm Syria's neighbors and fear of migrants has created a populist backlash threatening governments in Europe's democracies.
Massive assault
But Obama, who came to office vowing to shun the type of "dumb war" his predecessor started in Iraq, was reluctant to get involved and even declined to bomb Assad after chemical weapons strikes in 2013.
Washington's response was diplomatic, with US Secretary of State John Kerry working with Moscow to persuade Assad and the moderate opposition to declare a truce and launch political talks.
A ceasefire declared last month lasted barely a week, with Moscow and Washington blaming each other after it broke down and Assad launched a massive assault on rebel-held eastern Aleppo.
The Kremlin insists it is still willing to talk, but US officials now assume Moscow intends to secure Aleppo for Assad before approaching any dialogue with the next White House from a position of strength.
So in four months' time, what kind of reception will they get from a President Clinton or a President Trump?
Most observers expect Clinton to be more hawkish than Obama, having seen the failure of her attempt to "press the reset button" on ties with Moscow during her time as secretary of state.
Clinton's successor in the job was caught on tape last month lamenting that he had "lost the argument" for punitive action against Assad within Obama's cabinet.
Trump's position is less clear. He has staked out the case for an aggressive strategy, with up to 30,000 US troops, to destroy the IS group threat in Iraq and Syria.
But he has an ambiguous position on Assad and has stressed his willingness to work with Putin, while suggesting the US distance itself from its allies and stop being a world policeman.
"I think we have to get rid of ISIS before we get rid of Assad," he told the New York Times in July, using an alternate acronym for the jihadist group.
"Look, Assad hates ISIS. ISIS hates Assad. They are fighting each other. We are supposed to go and fight them both?"
And, campaigning in July, Trump said: "Wouldn't it be nice if we got along with Russia? Wouldn't it be nice if we got together with Russia and knocked the hell out of ISIS?"
For Danielle Pletka of the American Enterprise Institute, a conservative think-tank, neither candidate has a coherent strategy and both Russia and China are ready to take advantage.
"I don't think we can trust either of them," she said.
"If the last eight years have emboldened Putin and Beijing, I don't think there's any question that this instability, this indecisiveness, this waffling will embolden them even further."
