What begins? Russia’s GDP is less than both CA. and Texas. Turkey is a member of NATO for better or worse. Russian power stems more from myth than fact though they are a tough people when their backs are to the wall.
Russian arms to their BFF the Kurdish peshmerga for one. Cut's off Turkey's exports is another and stops the flow of gas. That is the best scenario - the other being is a nuclear exchange at the worst case scenarios.
No European will fight for Turkey - NATO charter not withstanding. Europeans hate Turks on an ethnic level. And I doubt most Americans would fight for Turkey either.