The kneejerk response of Turkey’s leaders to the country’s latest terrorist atrocity – Sunday’s suicide bombing in Ankara that killed 37 people and injured more than 100 – suggests that Recep Tayyip Erdoğan, Turkey’s strongman president, and his neo-Islamist party are fresh out of ideas about how to halt what looks increasingly like a slide into chaos.The bigger problem, for Turkey’s US and European allies, is how to shore up a strategically important Muslim democracy, Nato member and EU applicant that had long been considered a vital outpost of stability in a volatile region. Once-dependable Turkey seems in danger of implosion. Under Erdoğan, Turkey is the west’s disintegrating ally and Europe’s imaginary friend.This dilemma will come sharply to a head later this week when Angela Merkel, Germany’s chancellor, tries finally to seal an EU deal with Turkey on Syrian migrants. Erdoğan is demanding visa-free travel for Turks, accelerated accession talks and for Brussels to ignore human rights abuses in return for his cooperation. Several EU countries, notably France and Cyprus, are adamantly opposed.