Washington, DC – A lightning-quick offensive has seen Syria’s opposition take control of major cities and large swaths of territory, toppling the government of longtime leader President Bashar al-Assad and indelibly altering the war-torn country’s future.

The events represent a remarkable reversal of fortunes in Syria and enlivened a multipronged civil war that appeared largely stagnant for years. The situation, analysts told Al Jazeera, also appears to have been largely unanticipated by the administration of United States President Joe Biden, and raises galling questions over how Washington will proceed in the weeks and months ahead.

“I think everything that’s happening caught them by surprise,” Qutaiba Idlbi, a senior fellow at the Washington, DC-based Atlantic Council, told Al Jazeera. “So many of us analysts and Syria watchers have been wondering what’s going to come next.”

“[The Biden administration] will need to recalibrate their approach to Syria,” added Idlbi, who is also a Syrian refugee. But that is all but assured to be constrained by Biden’s diminished power before he hands over the office in January to president-elect Donald Trump, he said.

“I feel that the events on the ground are moving way too quickly for them to catch up, especially in this lame-duck session.”

‘Historic opportunity’ or ‘risk and uncertainty’?

Speaking on Sunday – hours after opposition groups led by Hayat Tahrir al-Sham (HTS) entered the Syrian capital of Damascus and sent al-Assad fleeing the country – Biden gave his first response to what he described as both a moment of “historic opportunity” and “risk and uncertainty”.

Biden said the end of al-Assad’s presidency was in part due to US support for Israel’s war on Gaza and its fight against Hezbollah in Lebanon, as well as support for groups in Syria and Iraq that weakened Syria’s close ally, Iran.

He also pointed to US support for Ukraine’s war against Russia’s invasion, which siphoned resources from Moscow, a close ally of al-Assad: “The upshot of all of this, for the first time ever, neither Russia [nor] Iran or Hezbollah could defend this abhorrent regime in Syria,” Biden said.

Looking ahead, Biden said Washington would prioritise supporting Syria’s neighbours – including Jordan, Lebanon, Iraq and Israel.

He said US forces would remain in northeast Syria, where they support the Kurdish-led Syrian Defence Forces against ISIL (ISIS). About 900 US troops are currently in the northeast of the country.

Finally, Biden pledged to engage “with all Syrian groups”, while vowing to “remain vigilant”.

“Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism,” he said.

A senior US official quoted by Reuters, however, said that HTS was “saying the right things”.

‘Six weeks left on the clock’

The first official response from the White House underlines several key questions that will determine the shape of US policy on Syria going forward.

But Biden – during his short time left in office – is unlikely to provide those answers, according to Aaron David Miller, a senior fellow at the Carnegie Endowment for International Peace and a former Middle East analyst at the State Department.

“You’re talking about an administration that has six weeks left on the clock,” he said. “And with six weeks left on the clock, I would just try to prevent and guard against potential complications or catastrophes.”

That means most major decisions will likely be made by Trump.

During his first term, Trump repeatedly sought to withdraw US troops from Syria. He appeared to re-up that effort on Saturday, writing on his Truth Social account that the US “would have nothing to do” with the country.

The Biden administration has also not articulated how it will mediate its support for the SDF’s fight against ISIL with the evolving landscape on the ground. Like other rebel groups, the SDF has seized new territory – including the eastern city of Deir Az Zor and the Abu Kamal border crossing with Iraq – in recent days.

Speaking to reporters last week, Pentagon spokesman Pat Ryder said US forces were not “participating in combined arms manoeuvre with the SDF” in their offensive.

But the fluid situation on the ground could see more opportunities for escalation between the SDF and the Turkish-backed Syrian National Army (SNA) group, according to analyst Idlbi.

“Of course, those questions are still pending,” he said.

The Biden administration is also widely expected to revisit its designation of HTS as a “terrorist organisation”, which could restrict US engagement with any fledgling transitional government.

Jabhat al-Nusra was formed in 2012 by ISIL but broke from the group a year later and pledged allegiance to al-Qaeda. It joined with other factions and broke from al-Qaeda in 2017, rebranding as HTS.

Its leader, Abu Mohammed al-Julani, whose real name is Ahmad al-Sharaa, has since portrayed himself as a supporter of pluralism and equality, but wariness remains for how the group would treat the vastly diverse communities that make up Syria’s population.

The US government continues to have a $10m bounty on his head.

‘Backburner’

Despite Biden’s celebration over al-Assad’s ousting, Idlbi said he remains wary that this was the outcome the administration wanted to see.

At the very least, he said the Biden administration had been caught flat-footed between diverging schools of thought: One that supported keeping al-Assad in power to avoid a vacuum, while coaxing him away from Iran, and another that supported wider regime change.

He pointed to a Reuters news agency report last week that said the US and United Arab Emirates had recently discussed the possibility of lifting sanctions on al-Assad if he agreed to pull away from Iran and cut off weapons routes to Hezbollah.

The principles of the Biden administration’s approach to the situation, with its deprioritisation of Syria since taking office in 2021, never fully took form, he added.

“Syria has been put on the back burner for the last four years, and the burner has been turned off,” Idlbi said.

In many ways, the muddied strategy has reflected US policy throughout the war, which saw support for some opposition groups fizzle into a diplomatic pressure campaign against al-Assad.

The administration of former US President Barack Obama had initially embraced opposition to al-Assad as similar popular uprisings stretched across the Middle East, supporting a coalition of rebel groups largely based in pockets of the country’s east and south.

That support involved a since-declassified CIA programme that saw the US, the United Kingdom and several Arab countries funnel money, weapons and training to some rebel groups. The programme has been criticised for inadvertently funnelling weapons to groups considered “terrorists” by the countries involved.

Obama also famously said that al-Assad’s use of chemical weapons against Syrians would constitute a “red line”, but he balked on direct military intervention following the government’s chemical attack on Ghouta in 2013. Four years later, Trump did strike a Syrian air base in response to the Khan Sheikhoun chemical weapons attack, the first US attack of its kind since the war began.

Speaking to Al Jazeera, Mahmood Barazi, the president of the American Coalition for Syria, a grouping of US organisations that has opposed al-Assad, said the quickly shifting situation has prompted him to rethink how to approach advocacy with the incoming Trump administration.

Given Trump’s unique mix of isolationism and hawkishness towards Tehran, Barazi had planned to focus on Iranian influence in Syria to convince officials of the need to turn the screws on al-Assad.

Now, he is trying to figure out the best way to “create a system with this administration to keep a very mindful and proactive approach towards Syria”.

“For me, this an opportunity,” he said.