Last week, it was a US troop pullout and an invitation to the White House. Now Donald Trump is slapping sanctions on Turkey. The US president's surprise decision to withdraw support for Syria's Kurds was taken as a green light by Ankara, which wasted no time crossing the border with the aim of establishing a buffer zone between itself and a group closely allied with its own PKK insurgency. Amid the uproar over abandoning the fighting force that took on the Islamic State group, we try to make sense of the US sanctions.