At the beginning of the week, the U.S. Treasury Department imposed sanctions on Turkey over its purchase of Russian S-400 missile defense systems.
New developments fuel tensions between Washington and Ankara. Despite U.S. President Donald Trump's promises to President Recep Tayyip Erdoğan over the phone, no problem has yet gone away. Quite the contrary, the foreign policy establishment and Congress continue to try and undermine bilateral relations.
The YPG is the Syrian arm of the outlawed PKK that has been fighting against the Turkish state for years, so it is impossible for Ankara to accept any presence of these militants near its borders