Washington realizes that Ankara is getting out of control and a robust military fist along the borderline will only assist Erdogan. U.S. support for the SDF has put enormous strain on ties with NATO ally Turkey, which views the YPG as an extension of the Kurdistan Workers’ Party (PKK) – a group that has waged a three-decade insurgency in Turkey and is considered a terrorist group by the European Union, Turkey, and the United States.
The Pentagon has lost access to NATO tactical nukes and the Inkrit airbase used to fight ISIS. A few interesting links to consider:
“A dual arrangement was then brokered by US Secretary of State Hillary Clinton between the Erdogan and Gulen factions in Turkey to split the illegal oil wealth captured by Islamic State terrorists in Iraq and Syria—and which Hillary Clinton has been paid by Gulen, to both her families foundation and presidential campaign, an estimated $1 million.”
In particular, study Victoria Nuland. In contradiction to the State Department, also note Josh Earnest, the White House spokesman, who cryptically calls the consequences of not removing Syrian President Assad "quite grave." It is unknown if the White House was aware of the visit. All we know now is that it involved a US-Russian alliance in fighting ISIS.