Erdogan might propose a withdrawal from the NATO at this rate. That's pretty serious if you ask me.
My belief is that Turkey needs NATO more than NATO needs Turkey. While it is the second largest contributor to NATO after the US, it is also the second largest military force in NATO by numbers - so it's contribution is only proportionate to its presence.
Leaving NATO means jeopardising access to sensitive arms systems, technology and training that at this juncture I feel would hurt Turkey. The leading European nations are prosperous enough to increase their spending if needed.