By David E. Sanger

WASHINGTON — For years, the American strategic map of the Middle East was dominated by Iran at the centre of power of a ‘Shiite crescent’, with Syria as the funnel for Iranian arms used by terrorist groups to attack Israel, and as the home to Russia’s naval and air presence in the region.

Yet when the Syrian government fell with astounding speed over the weekend after more than a half-century of rule, shattering yet another crucial element of the crescent, US intelligence officials were caught by surprise. As recently as Friday (6) night, senior US officials thought President Bashar al-Assad had a roughly even chance of holding on — even if that meant reaching for the chemical weapons he had used on his own people.

Washington awoke Sunday (8) morning to a new reality. It is perhaps the most momentous upheaval yet in the 14 months since Hamas’ Oct. 7, 2023, attack on Israel unleashed a wave of violent retaliation that changed the region’s power dynamics.

Now, with Assad’s ouster, two urgent and related questions are circulating through Washington, just six weeks before the inauguration of President-elect Donald Trump for his second term — one in which the world looks dramatically different than when he left office just shy of four years ago.

First, will the rebels evict the Iranians and the Russians from Syrian territory, as some of their leaders have threatened? Or, out of pragmatism, will they seek some kind of accommodation with the two powers that helped kill them in a long civil war?

And will the Iranians — weakened by the loss of Hamas and Hezbollah, and now Assad — conclude that their best path is to open a new negotiation with Trump, only months after sending hit men to kill him? Or, alternatively, will they race for a nuclear bomb, the weapon some Iranians view as their last line of defence in a new era of vulnerability?

It may be months before the answers to either of these questions become clear. But where things go next may well determine whether Sunday represented a day of liberation and the start of a rebuilding — or the prelude to more military action.

Before the fall of Damascus, Syria’s capital, the leader of Hayat Tahrir al-Sham (HTS), the formerly al-Qaida-linked rebel group that led the lightning strikes on Assad’s government, told a CNN interviewer that “the revolution has transitioned from chaos to a sense of order.”

But the leader, Abu Mohammed al-Golani, who is still sought by the United States as a terrorist, gave no indication of how the group might try to govern. “The most important thing is to build institutions,” he said, suggesting that he now wanted a society to which displaced Syrians would want to return and rebuild. “Not one where a single ruler makes arbitrary decisions.”

As Dan Shapiro, a former US ambassador to Israel and now a senior Pentagon official with responsibility for the Middle East, put it, “No one should shed any tears over the Assad regime”. At least 580,000 people died in the first decade of the civil war that began in 2011, the United Nations High Commissioner for Refugees estimated three years ago, and millions have been injured or displaced.

But it is one thing to celebrate the ouster of Assad, who Russian state television said arrived in Moscow on Sunday. It is another to manage the vacuum of power that follows — and to make sure that Syria becomes neither a terrorist state of a different kind nor a failed state, as Libya did after Moammar Gadhafi was deposed and killed 13 years ago.

President Joe Biden acknowledged as much after declaring from the Roosevelt Room of the White House on Sunday afternoon that the “moment of opportunity” before the world was “also a moment of risk and uncertainty, as we all turn to the question of what comes next”.

“Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism and human rights abuses,” he said. He noted that leaders like Golani were “saying the right things now, but as they take on greater responsibility we will assess not just their words, but their actions”.

That assessment, though, will fall largely to Trump’s administration. And it will test the meaning of his social media postings claiming that the best strategy is for the United States to stay out.

Trump is unlikely to have that luxury. The United States has a military force of 900 in eastern Syria, hunting down and striking Islamic State group forces. And while Trump’s instinct in his first term was to pull out, he was convinced by his military advisers that a US withdrawal from its Syrian base could cripple the effort to contain and defeat Islamic State group forces.

On Sunday, as Assad fled, the United States targeted gatherings of Islamic State group fighters, dropping bombs and missiles in a counterterrorism effort that officials said had no relation to the fall of Damascus. A senior administration official told reporters Sunday that it was a “significant strike”.

And whether Trump acknowledges it or not, the United States has huge interests in whether Russia gets ousted from its naval facility at Tartus, its only Mediterranean port to repair and support Russian warships. “For Russia, Syria is the crown jewel of their launchpad to becoming a great power in the region, an area that has traditionally been a US sphere of influence,” said Natasha Hall, a Syria expert at the Centre for Strategic and International Studies in Washington.

Russia also used a Syrian air base to kill thousands of Syrians who opposed Assad. In an era of new cold wars, where Russia is seeking to expand its influence, the possibility that Moscow might permanently lose access to Syria could be of huge strategic advantage to the United States. It will also be an interesting early test of how Trump handles President Vladimir Putin of Russia at a moment when negotiations over the fate of Ukraine may be about to begin.

But the bigger question is how the incoming president will deal with Iran. In recent weeks, he has expressed interest in a new negotiation with Iran, six years after he terminated the 2015 nuclear deal with the country. The Iranians have shown some interest in engaging, as well — though it is not clear they are willing to give up the nuclear program in which they have invested so much in the past few years.

The risk is that Iran’s leaders could decide that the country is so weakened — its proxies crippled, its pathway to ship arms through Syria imperilled, its air defences wiped out in recent Israeli strikes — that it needs a nuclear weapon more than ever.

Clearly, the Iranians were as stunned this weekend as everyone else. Iranian Foreign Minister Abbas Araghchi, appearing on state television, said Iran had been caught off guard by the speed of events. “Nobody could believe this,” he said.

Iran is closer to a nuclear weapon than at any point in the 20 years of Iran’s efforts to build its nuclear capabilities. On Friday, Rafael Grossi, director-general of the International Atomic Energy Agency, the United Nations’ nuclear watchdog, said that Iran had undergone a “dramatic acceleration” of its production of near bomb-grade uranium. It has enough of a stockpile to build four bombs, though fashioning them into a warhead could take a year to 18 months. Grossi’s statement suggested that it was now moving at a pace that would enable the production of many more.

That could just be a bargaining ploy. But clearly the Iranian leadership is under pressure, and the fall of a longtime ally and supplicant like Assad is likely to make some Iranian leaders worry whether the same fate could be awaiting them. Whether that new insecurity leads them to negotiate their way out of a hole or obtain the ultimate weapon of survival, is one of the many mysteries ahead.

People celebrate the fall of Syrian President Bashar al-Assad’s government, on a road that leads to the Masnaa border crossing with Syria, in Bar Elias, Lebanon, on Sunday (Dec. 8, 2024). Assad’s overthrow could mean Russian bases in Syria are closed and Iran’s pathway to Hezbollah is cut off — and newly vulnerable Iran may have to decide between negotiating with President Donald Trump and racing to build a nuclear bomb -Daniel Berehulak /The New York Times