The Islamic State group's defeat in Raqa, their de facto Syrian capital, raises a thorny question for the US forces that have been training and arming the victorious local fighters: What comes next?
Since the US began bombing IS in Syria in late 2014 and supporting a predominantly Kurdish ground force, two successive administrations have side-stepped addressing America's long-term military role in Syria, saying only that the focus is on killing jihadists.
Critics say America is losing leverage in the knotted conflict and has failed to properly engage, opting instead for the simpler narrative of viewing Syria's violence only through the prism of a counterterrorism operation.
"What we need instead is a comprehensive strategy that takes all regional factors into account," Senator John McCain, who heads the Senate Armed Services Committee, said this week.
We need "a clear articulation of our interests and the ways and means we intend to secure them. The absence of such a strategy is acutely felt even as we celebrate this important success" in Raqa, he added.
Syria's conflict began in March 2011 with anti-government protests, but quickly spiraled into a bitter and complex civil war, with IS just one element in a shifting matrix of players.
About 900 US ground troops, the bulk of them special operations forces, are in northern Syria, where they have provided critical support to a Kurdish and Arab coalition called the Syrian Democratic Forces (SDF).
The alliance has benefited from weaponry and technical know-how, with US commandos training the locals on how to call in air strikes.
They get constant support from US-led coalition planes and drones, and the Pentagon sent a Marine artillery to help near Raqa, while US forces also expanded a runway for military cargo planes at a northern Syria air base.
Militarily, the anti-IS fight in Syria is not quite over, with the jihadists still entrenched in towns and villages along the Euphrates River Valley.
The jihadists have lost nearly all the territory they once controlled in Iraq and Syria, but are also establishing footholds in other countries such as Yemen and Afghanistan.
Towns abandoned by IS are littered with explosives, mines and booby traps.
We'll "support the stabilization efforts in Raqa, and other liberated areas, to include the removal of explosives left behind by ISIS, restoring basic services, and supporting local governing bodies," State Department spokeswoman Heather Nauert said.
President Donald Trump, who has spoken little about Syria or hinted at any sort of broader long-term strategy, faces a situation far different from when Barack Obama commenced military operations in Syria.
Russia joined the conflict in late 2015, quickly tipping it in favor of President Bashar al-Assad, while the influence of Iran and Tehran-backed militias also grew rapidly.
For John Hannah, senior counselor for the Foundation for Defense of Democracies and former national security advisor to vice president Dick Cheney, Raqa's recapture is not likely to mark the end of US involvement in Syria.
He said Trump's tough line on Iran -- the president last week refused to certify the Iran nuclear deal -- must translate to action to stem Tehran's influence in Syria.
"If President Trump's strategy for countering Iran is to have any meaning at all, it must almost certainly include a robust effort to contain and constrict the IRGC's commanding role in Syria," Hannah told AFP, using the abbreviation for the Iran's Islamic Revolutionary Guard Corps.
"That means preventing Iran, Hezbollah and their Shiite proxy militias from having unchallenged control of eastern Syria and the Iraqi-Syrian border that are vital to Iran's strategic goal of establishing a land bridge from Tehran to the Mediterranean and the Israeli border."
Such an outcome could start the countdown to an Israel-Iran conflagration, he warned.
Jon Alterman, Middle East program director for the Center for Strategic and International Studies, said the United States must decide how much it cares about different Syria outcomes, including how much of a presence Russia and Iran have.
"Negotiations will determine Syria's future, and the United States hasn't done much to maximize its leverage in those negotiations," Alterman told AFP.
He noted the US could engage on several fronts, but "there's not much public support for that, and the Trump administration may decide it's not worthwhile."
Hannah also noted that with US-backed forces now controling large parts of Syria, the US potentially has a source of diplomatic leverage in shaping Syria's post-IS future.
But Nauert indicated America may only be playing a limited role.
"Our goal and mission right there in Syria is to defeat ISIS. That is exactly why ... the US government is engaged in Syria, and that's really to defeat ISIS," she said.
For now at least, the Pentagon won't discuss what role US troops will have after the defeat of IS, saying it would be premature to do so until the job is done.