Russia and Turkey are systematically excluding the United States from events in Syria. The US must either demand a seat at the table, shaping negotiations, or cede diplomacy to Russia and Turkey, knowing they will act in their narrow national interests to the detriment of Syrians.
Collusion between Russia and Turkey has been underway since August 8 when Vladimir Putin and Tayyip Erdogan met in St. Petersburg to normalize relations. Their collusion intensified after the assassination of Russia's Ambassador to Turkey, Andrey Karlov.
Russia and Turkey coordinated their response to Karlov's killing, calling it a provocation "to spoil Russia-Turkey ties" and undermine "the peace process." They announced a joint commission to investigate the assassination.
Russia and Turkey orchestrated the evacuation of eastern Aleppo -- without informing the US.
The foreign ministers of Russia, Turkey and Iran endorsed the "Moscow Declaration." Neither Secretary of State John Kerry nor UN officials was invited to discuss the road-map to end Syria's civil war at the conference in Moscow on December 20.
Today's announcement that Russia and Turkey are working towards a cease-fire is no surprise. It merely formalizes what was apparent.
It's time for a steely-eyed assessment: Tayyip Erdogan is at best an uncertain ally; Vladimir Putin is a strategic adversary. Both are unprincipled pragmatists, colluding to advance their national interests at the expense of the United States.
Erdogan was initially committed to overthrowing Syria's President Bashar al-Assad. Turkey provided logistical support, weapons and money to radical groups such as the Islamic State. However, Russia's entry into the war turned the tide against the proponents of regime change.
In response, Erdogan shifted Turkey's priority from overthrowing Assad to constraining the Syrian Kurds. He fears that the establishment of contiguous Kurdish territory in Syria along Turkey's border would destabilize Turkey, inspiring greater demands by Turkish Kurds.
Turkey's launched "Operation Euphrates Shield," invading Jarablus and pushing south to Al-Bab. Turkey called it a counter-terrorism operation, but the invasion of Syria is really intended to block Kurdish ambitions.
Russia and Turkey have reached an understanding. Turkey would be silent in the face of Russia's actions in Aleppo. It would abandon demands for regime change in Damascus, and end support for certain jihadi groups threatening Assad. In turn, Russia would turn a blind eye to Turkey's illegal occupation aimed at establishing a "safe zone" inside Syria.
Putin was furious when Turkey downed a Russian Sukhoi-24 in November 2015. He called it a "stab in the back" and launched an economic embargo. The boycott was short-lived. When Putin and Erdogan met on August 8, they agreed to resume economic cooperation and normalize relations.
Putin and Erdogan have adopted their own cynical real-politic. On the 100-year anniversary of the Sykes-Picot Agreement, which carved up the Ottoman and Habsburg empires between Western Powers after the First World War, Russia and Turkey have agreed on spheres of influence in Syria.
The Obama administration's response has been muted. Without boots on-the-ground, America has little leverage in Syria. Russia and Turkey have filled the gap, aligning their interests to the exclusion of the United States.
Russia and Turkey have marginalized and maligned the United States. Erdogan pronounced at the UN Security Council, "The world is bigger than five." Turkish officials suggested that Washington was behind Karlov's killing in order to drive a wedge between Russia and Turkey. Russia's Foreign Minister Sergey Lavrov disparaged the Obama administration for "idle chatter."
America's marginalization has been ongoing since 2012, when President Obama disappointed Assad's opponents by refusing to get militarily involved.
What about America's future role? President-elect Donald J. Trump is enamored with Putin. National Security Adviser Michael Flynn is a bedfellow of Erdogan. Given their affinities, Russia and Turkey can expect free reign to entrench Assad's rule and target Sunni rebels.
Declaring peace does not mean there is peace. Count on the Islamic State to keep fighting. US-backed Syrian Democratic Forces, which include Arab and Kurdish militias, are engaged in a battle for Raqqa, the ISIS capitol. They are not about to lay down their weapons and have a tea party with Islamic State hard liners. Too many have sacrificed too much to simply surrender and wave a white flag.
Surrendering the field to Russia and Turkey would be a blow to US strategic interests. Emboldened by Turkey's fealty, Putin could test NATO commitments in the region, seizing lands in Eastern Ukraine and threatening Poland and the Baltic States. Would Turkey block NATO's response? Will it deny access to Incirlik Air Force Base on NATO's eastern flank? Europe's security architecture will be in shambles if Turkey allies with Russia.
In addition, Russia and Turkey risk a spiral of deadly violence domestically. About 14 percent of Russia's population is Sunni Muslim. Kurds represent at least 20 percent of Turkey's population. Both are embittered by indiscriminate counter-insurgency measures targeting Sunnis and Kurds in Syria.
Turkey's realignment with Russia would also have an economic cost. Siding with Russia would indefinitely delay Turkey's EU membership. Turkey could turn to the Shanghai Cooperation Organization as a substitute for European integration, but no windfall will come from business with cleptocracies.
There is no military solution to Syria's civil war. Fighting will only stop through negotiations that preserve Syria's sovereignty and devolve power from Damascus to Syria's regions with security and political guarantees from the international community.
The US is at a fork in the road. Will Washington retreat, confirming its decline? Syria is a proving ground, testing US leadership in the Middle East and around the world.
Mr. Phillips is Director of the Program on Peace-building and Rights at Columbia University's Institute for the Study of Human Rights. He served as a Senior Adviser and Foreign Affairs Expert at the US Department of State during the Clinton, Bush and Obama administrations.