Finally, Turkey seems to believe that despite its policy of active neglect as the Islamic State shells the Kurds in Kobani, the P.K.K. will not terminate the prevailing cease-fire and decide to fight both Turkey and the Islamic State at the same time.

This assumption is now undergoing a stress test. Many Kurds have decided to demonstrate their dissatisfaction with violent street protests, forcing the government to declare a curfew, for the first time in many years, in five predominantly Kurdish cities in Turkey’s southeast. They blame the Turkish government for not doing enough to save Kobani and for hindering Kurdish efforts to bring aid and fighters to the enclave from across the Turkish border. The Kurdish leadership even threatened to pull out of the talks should Kobani fall to the Islamic State. Indeed, the peace talks with the P.K.K. that until recently seemed on track are now at risk of derailing.

Even riskier is the policy decision Turkey’s leaders have taken in the past week. The Parliament adopted a bill allowing the government to send troops to Iraq and Syria to fight terrorism. This was rightly interpreted in the West as a belated commitment by Turkey to be part of the anti-Islamic State coalition. But Ankara is demanding Washington’s support for regime change in Syria before engaging itself more substantively in the fight against the Islamic State.

Turkey sees the Islamic State as a symptom rather than the cause of the problems that bedevil the Middle East. It believes that only a comprehensive and ambitious campaign targeting the Assad regime can help to stabilize the region in the long term. Hence Turkish leaders are demanding safe havens and no-fly zones within Syria. These protected areas would cater to the accommodation needs of future waves of refugees but also serve as an assembly and training zone for more moderate Syrian opposition fighters.

But Turkey’s stubborn emphasis on regime change in Syria is finding little support in Washington. For the United States and for much of the Western world, the Islamic State remains the core threat. Therefore Turkey’s policy of conditioning its anti-Islamic State engagement on support for an anti-Assad campaign will be at best ineffective and at worst counterproductive.