“In recent weeks, a Turkish backed umbrella group dubbed Jaysh al-Fateh has taken control of Idlib, prompting speculation that the group’s recent advance could mark a turning point in the war. These recent successes are widely attributed to a rapprochement between Saudi Arabia and Turkey – two critical regional players in Syria that had hitherto supported different factions in northern Syria.
The United States has quietly acquiesced to the resurgent Saudi-Turkish role in Syria, but the prevalence of al-Qaeda affiliate Jabhat al Nusra and ally Ahrar al-Sham in recent offensives will certainly complicate on-going discussions about whether to provide air cover for rebel battalions in the north. This key divergence could further complicate US-Turkish relations, despite the recent agreement to train-and-equip up to 15,000 Syrian rebels in Turkey, Jordan, and Saudi Arabia.”
IR Theory & Practice 