As the prospect grows of military confrontation with\u00a0Russia\u00a0in the skies over Syria, the US is counting on support from European partners such as France and the UK. But help from a key regional ally \u2013 Turkey \u2013 is less certain, despite its position on Syria\u2019s northern border and opposition to Bashar al-Assad\u2019s regime.\r\nThere are echoes of 2003, when Turkey refused to back the US-led invasion of Iraq. Whose side\u00a0Turkey\u00a0is on is a question increasingly exercising Washington policymakers as Recep Tayyip Erdo\u011fan, Turkey\u2019s president, builds closer ties with Russia.\r\nAlthough Turkey is a Nato member, its growing defence cooperation with Moscow includes a\u00a0recent $2bn deal\u00a0to buy state-of-the-art S-400 surface-to-air missile systems. At the same time, military collaboration with the US has been scaled back.\r\nFaced with Turkish restrictions, US air force combat operations at the Incirlik base, close to Syria\u2019s border, have been run down. In January a squadron of A-10 \u201cWarthog\u201d ground-attack jets was\u00a0redeployed to Afghanistan, reportedly leaving only refuelling aircraft at the base. Last year Germany, another Nato member, was obliged to withdraw its forces from Incirlik amid a fierce row with Erdo\u011fan over human rights and legal issues. The German aircraft, which like their American counterparts were engaged in attacking Islamic State forces in Syria and Iraq, were\u00a0moved to Jordan.\r\nUS-Turkey tensions rose after the\u00a0failed 2016 coup attempt\u00a0in Ankara, which Erdo\u011fan claimed was instigated by opponents based in the US. They have since been exacerbated by rows over Turkish human rights abuses, Washington\u2019s support for\u00a0anti-Assad Syrian Kurdish forces, whom Turkey regards as terrorists, and by Turkey\u2019s military incursion into Afrin, in north-west Syria.\r\nErdo\u011fan\u2019s government, which has previously demanded Assad step down, initially blamed the Syrian regime for last Saturday\u2019s chemical weapons attack in Douma \u2013 the focus of current tensions between Russia and the west. \u201cThe Syrian regime will have to pay the price,\u201d \u0130brahim Kalin, Erdo\u011fan\u2019s spokesman, said on Monday.\r\n\u00a0\r\nThe government spokesman Bekir Bozda\u011f said the Assad regime was\u00a0guilty of \u201cbarbarity\u00a0and [a] crime against humanity\u201d. But Ankara changed its tune after Erdo\u011fan received a phone call later that day from Assad\u2019s main backer, the Russian president, Vladimir Putin. Ensuing official statements pointedly avoided blaming Douma on the regime,\u00a0calling instead for a \u201ccareful investigation\u201d\u00a0\u2013 Putin\u2019s exact position.\r\nA menacing statement by Sergei Lavrov, Russia\u2019s foreign minister, may also have changed Turkish minds. Russia has hitherto acquiesced in Turkey\u2019s Afrin operation, obtaining assurances from Damascus that regime forces would not oppose it. But on Monday Lavrov said Moscow expected Turkey to hand over Afrin to Assad. Iran, Russia\u2019s collaborator in\u00a0Syria, made a similar call. Erdo\u011fan angrily rejected the demands, but the message from Moscow was crystal clear: don\u2019t mess with us.\r\nTurkey\u2019s close collaboration with Russia \u2013 critics would call it subservience \u2013 is a relatively recent phenomenon. The two countries came to blows in November, 2015 when Turkey shot down a Russian military jet for alleged airspace violations. Moscow retaliated by imposing economic sanctions.\r\nTo the dismay of Nato and the EU, the subsequent rapprochement has been rapid, fuelled by shared self-interest, especially in Syria. Both Erdo\u011fan and Putin want to shape any post-war settlement to their advantage. To this end they launched, with Iran, the so-called Astana peace process, rivalling talks overseen by the UN.\r\nPutin personally commiserated with Erdo\u011fan after the 2016 coup attempt, assuring him of Moscow\u2019s full support. That was an important moment for two instinctive autocrats who fear the popular verdict of the street. Since then, bilateral cooperation on nuclear power, energy pipelines from Russia to Turkey and Europe, tourism, investment, arms sales and military-to-military ties\u00a0have reached \u201cunprecedented levels\u201d, according to the IISS thinktank.\r\nErdo\u011fan and Putin share another aim: curbing US influence in the Middle East. And for Russia, courting Turkey brings additional benefits \u2013 sowing discord within Nato and limiting US military options in Syria when, as now, push may come to shove.