Turkey controls whether Russian warships can transit from the Mediterranean into the Black Sea. Russia’s easiest move here is to either buy their way past Turkey, which is in terrible economic condition, or create political chaos in Turkey. Posit for a moment that the Turkish president dies. There would probably be turmoil exacerbated by Russia. In the confusion Russia could move something like twenty-plus warships into the Black Sea. This might be enough to tip the military balance as those ships have been loitering in the area of the straits since the conflict began, just waiting for something to happen so they can move in.
Turkey may be playing with fire.
I believe the Turks have a sizeable Black Sea fleet as well, and certainly many aircraft that can fly from Turkey. Plus the Turks could also go after Russian assets in the Med and Syria. It wouldn’t be a pushover for the Russians.