The United States and Russia have agreed on a plan that, if implemented, could “provide a turning point, a moment of change” in the Syria war, according to US Secretary of State John Kerry.

If it works, the deal would indeed be a breakthrough. Turkey, the European Union, the United Kingdom and the Syrian National Coalition have welcomed the agreement. US diplomats have succeeded in putting the onus on Russia to assure that the Syrian government does not fly combat missions against opposition forces backed by the United States and its allies. The cessation of hostilities would be renewed and after a period of reduced violence, the United States and Russia would begin joint planning against Jabhat al-Nusra, now known as the Jabhat Fatah al-Sham (Conquest of Syria Front), al-Qaeda’s affiliate in Syria. UN-mediated talks on a political transition would resume as soon as possible.

In his press conference Sept. 9, Kerry went on the offense against skeptics, critics and dissenters within the US government and elsewhere. “Going after Nusra is not a concession to anybody,” he said. “It is profoundly in the interests of the United States to target al-Qaeda — to target al-Qaeda’s affiliate in Syria, which is Nusra, an organization that is opposed to a peaceful transition, an organization that is an enemy of the legitimate opposition, an organization that is currently plotting attacks beyond Syria’s borders, including against the United States.”

While Russia will rightly be held accountable for Syrian President Bashar al-Assad’s compliance, the deal could also depend on the willingness of regional parties allied with the United States to compel their armed proxies in Syria to separate from Jabhat al-Nusra. Disentangling these armed groups from Jabhat al-Nusra had been a sticking point in US-Russian negotations, but Kerry said Sept. 9 that the game is up. He warned those “opposition groups who have up until now found it convenient to sort of work with them [Jabhat al-Nusra] … it would not be wise to do so in the future. It’s wise to separate oneself. And indeed, that will be different. There is a deterrence in that. There is also a deterrence in Russia holding Assad accountable for his promise. And so this is a new equation, and we believe that this new equation offers an opportunity — again, not a certainty, an opportunity — for people to be able to find a peaceful solution because we don’t believe there is a military solution. And the current trend is simply creating more terrorists, more extremists and destroying the country in the process.”