This has already changed the course of the Syrian war. Turkey grudgingly accepted the fall of Aleppo in return for a de facto recognition of its zone of influence along the Syrian-Turkish border. Instead of supporting rebel groups fighting in Aleppo or pressuring the Assad forces besieging the city, Turkey raced to capture territory from the Islamic State before the Kurds did.
The Kremlin is now not only acting like the magnanimous victor in Syria, but also posing as the sole mediator between Ankara and Mr. Assad’s government and Iran. This month, Moscow hosted a meeting of the foreign and defense ministers of Russia, Iran and Turkey at which they discussed the future of Syria. This was a sign of things to come.
First Russia outwitted and sidelined the United States, the European Union and the United Nations. Now it is shaping the future of the conflict. The cease-fire that it has brokered is meant to manage rivalries in Syria and wind down the war on Russian and Mr. Assad’s terms. Moscow has suggested that the cease-fire be followed by political discussions with select groups of the Syrian opposition. But for this to work, Russia needs Turkey to deliver parts of the Syrian opposition that will accept considerably less than Mr. Assad’s departure.
Mr. Assad may not like it, but he is likely to accept this Russia-run process as a necessary evil. He has to play nice with President Vladimir V. Putin, his savior, even if he won’t concede much. Bringing Turkey on board is necessary to jump-start a peace process that will gut whatever is left of the United States and United Nations effort once meant to bring about a political transition — and Mr. Assad’s departure. What’s more, it would tie the hands of the Trump administration. Should the cease-fire collapse, the Assad government would still be able to crush the remnants of the rebellion with Russian cover. This arrangement will also prevent Kurdish autonomy — something that Mr. Assad, Iran and Russia, and Turkey all oppose.
All this leaves Qatar and, more important, Saudi Arabia with very little to work with. Both countries have in the past had to move weapons and money through Jordan and Turkey to support the rebellion; these routes are now difficult if not impossible. Unable to shape the battlefield or steer diplomacy, a bruised and overextended Saudi Arabia has quietly pushed Syria down its list of priorities.
The two Gulf states also understand that Turkey won’t subordinate its interests to their desires. In fact, Turkey is now arguing that its involvement in the Russia-led diplomacy is essential to check Iran’s ambitions, secure the withdrawal of Hezbollah and other foreign Shiite militias from Syria and obtain assurances that Mr. Assad will eventually be eased out. Turkey is seeking to include Qatar and Saudi Arabia in this process, to the displeasure of Iran.
None of these countries are likely to fully abandon what remains of the Syrian rebellion. The costs of doing so would be immense: their reputations would suffer greatly, and they would forfeit cards essential to influence the direction Syria takes. And Syrian rebels won’t disappear just because they were defeated. Instead, formal support and funding is likely to continue but at decreasing levels and with more modest objectives. Turkey still needs rebel muscle to fight the Islamic State and the Kurdish guerrillas. Saudi Arabia and Qatar can’t afford to be accused of having abandoned their Sunni brethren at a time of regional polarization.
They will also resist efforts by a number of Western, Asian and Arab countries to normalize relations with Mr. Assad. In their eyes, he remains a hostile actor who should be isolated and pushed out. How and when are questions for another day.