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Uruguay's U.N. Ambassador Elbio Rosselli, current president of the Security Council, speaks during a news conference following a closed meeting of the council on Monday, Jan. 4, 2016

It took a little over two weeks for a diplomatic breakthrough on Syria to break down.

After Saudi Arabia executed a prominent Shiite cleric on Saturday, Iranian protesters stormed its embassy in Tehran, leading Riyadh and several other Sunni-majority Muslim governments to cut diplomatic ties with Shiite Iran. The rivalry between the Saudi monarchy and Iranian theocracy — thinly veiled in conflicts from Bahrain to Yemen to Iraq — now threatens a narrow path to peace in Syria.

That roadmap, unveiled Dec. 18 as a unanimous Security Council resolution, was touted by the U.S., Russia, and others as the first real breakthrough in the nearly half-decade-old Syrian civil war because it was the first one backed by the biggest players on opposing sides of the conflict: Saudi Arabia, which supports the rebels, and Iran, which supports strongman Bashar al Assad.

But the resolution’s goals depended on a joint effort by Riyadh and Tehran to help usher the various parties to the bargaining table and meet an ambitious, roughly two-year timeline for elections. That effort now seems in doubt.

Related: US Syria Policy Shifts From ‘Assad Must Go’ to ‘Not Right Now’

Still, Saudi Arabia insists the escalating crisis won’t further disrupt a process that was already bound to have its bumps. (For one, Russia and the U.S. can’t even agree on who is a rebel and who is a terrorist, and thus, who can attend the talks.) “From our side it should have no effect because we will continue to work very hard to support the peace efforts,” said Abdallah Y. Al-Mouallimi, the Saudi ambassador to the U.N.

For now, the U.S. is trying to stay out of it, a balancing act it likely can’t keep up for long. On Monday, State Department spokesman John Kirby put on a brave face, insisting that the U.S. is confident that peace talks will start as planned in Geneva on Jan. 25. “We have consistently urged everyone to de-escalate tensions in the region so that we can all continue to work on resolving the pressing issues in Iraq, in Syria, in Yemen, and elsewhere throughout the Middle East,” Kirby said, but added, “Ultimately, solutions to problems in this region must come from leaders in this region … If you are asking whether we are trying to become a mediator in all this, the answer is no.”

Meanwhile, 2016 candidates, lawmakers, and administration critics are urging the U.S. to side with Saudi Arabia, a key ally in the U.S.-led fight against the Islamic State, even as the Obama administration tries to preserve a landmark nuclear agreement with Iran, which the president considers a key achievement of his tenure.

“Saudi Arabia is one of America’s closest and oldest partners and deserves our continued support,” Senate Armed Services Committee Chairman John McCain, R-Ariz., said in a statement Monday. “The Ayatollah’s feigned outrage is yet another example of the Iranian regime’s efforts to manipulate Shiite Muslims across the region to advance its self-serving agenda for power and regional hegemony. Tensions between Riyadh and Tehran have been escalating for years, due in no small part to the perception that America is withdrawing from the region.”

Wherever the Obama administration comes down, the Saudi-Iran falling-out seems likely to doom Syria to more years as the battleground for the region’s proxy wars — and a fertile haven for terror groups such as ISIS.

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