NATO is defensive. I believe that if a member starts something, there is no obligation to defend it.
Defending your airspace counts
The downing of a Russian plane in Turkish act is a defensive act
If NATO is half-way smart, they will abandon Turkey immediately. As much as any neighboring nation, Turkey has provided help, logistics and a clandestine trading partnership with the Islamic State, enabling them to expand and have some degree of territorial sanctity.
The present leadership of Turkey WANTS the development of a Caliphate, as part of restoring the old Ottoman Empire, which, until the revolt of “the young Turks” was a theocratic dictatorship, in all respects a caliphate, that was constantly at war with either Russia or Greece, and conducted one of the most massive of genocides against the Christian Armenians, that the world had seen up until that time.
When the revolt of “the young Turks” was over, the remaining parts of the former Ottoman Empire has become a hodgepodge of secular nations, free of the yoke of the theocracy that had dominated the territory since the fall of Byzantium. But this group of secular nations, having no history of rule by parliaments or any elective posts, soon became various suzerainties under the rule of strongmen, that fell prey to colonial conquests by France, England and Russia, countries which had a heyday carving up the land into various artificial territories, without regard to the tribes and nomadic cultures that lived there.
Turkey was once regarded as “the sick old man of Europe”, and by all odds, has suffered a serious relapse of that same sickness.