Al Qaeda has thrived in Syria thanks to the continued political survival of Syrian President Bashar Assad and Washington's failure to adequately support the revolution's more moderate opposition groups, Syria expert Charles Lister wrote Wednesday.

"The principal benefactor of Assad's survival is not Assad, nor Russia, Iran, Hezbollah or even ISIS — it is Al Qaeda," Lister, a senior fellow at the Middle East Institute and author of "The Syrian Jihad," wrote in The Daily Beast.

"Having spent the past five years embedding itself within broader revolutionary forces and strategically choosing to limit and very slowly reveal its extremist face, Al Qaeda's Syrian affiliate Jabhat al-Nusra is reaping the rewards of our failures to solve the Syrian crisis," Lister added. His research on Syria's antigovernment insurgency has involved direct engagement with the leadership of more than 100 opposition groups from across the country.

A proposal for stepped-up coordination between the US and Russia against Nusra in Syria — which would involve enhanced sharing of information about the group's positions — was confirmed Wednesday in a phone call between Russian President Vladimir Putin and US President Barack Obama.

But the new initiative is more likely to enhance than hinder Nusra's momentum in Syria, where the group has "accepted more than 3,000 Syrians" in the country's Idlib and Aleppo provinces in the past five months.

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Experts say any perceived coordination between the US and Russia is likely to increase the opposition's disenchantment with the West.

Rebels have expressed concern that weakening Nusra would strengthen Assad. And in its campaign to eliminate Syria's "terrorists," Russia has primarily bombed moderate opposition factions and civilian targets, including hospitals, schools, and bakeries.

"The continuing mingling in places of the so-called moderate opposition" with Nusra is "complicating antiterrorist action," Kremlin spokesman Dmitry Peskov said last month.

Acquiescing to a central Russian request, the US reportedly has begun urging rebel groups to leave areas where Nusra is present so Russian warplanes can target Nusra without hitting the mainstream opposition. To that end, the US has demonstrated that it is more willing to work on the Kremlin's terms than on those of the rebels.

Ultimately, many experts say, the opposition groups Russia has relentlessly targeted since late September 2015 are the only actors on the ground capable of challenging the influence Nusra is trying to cultivate among Syria's Sunni Arab population. Accommodating Moscow's demands in the war, then, is seen as a "slippery slope" that is more likely to serve Nusra's interests than those of the US.

'Adverse consequences galore'

Nusra's rise has boxed Washington into a Catch-22: To coordinate with Russia against Nusra would be to legitimize Assad's rule, fuel Al Qaeda's narrative, and ensure the continuation of the war. To spare Nusra and increase support for the opposition, on the other hand, would infuriate the regime and its allies and lead them to double down on the battlefield.

Emile Hokayem, a Middle East expert at the International Institute for Strategic Studies, said on Twitter that Obama's proposal to coordinate with the Russians was likely to have "adverse consequences galore."

"Obama resisted entanglement in Syria only to embrace entanglement w/ Russia there, probably making everything worse. Do Kerry and the geniuses at the White House realize that coordinated bombing of Nusra under current circumstances will actually benefit Nusra?" he wrote, referring to Secretary of State John Kerry.

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