Not nearly to the degree that Hillary or Obama would be a disaster for this country.
But since I am a Conservative, and McCain is not, even with an (R) after his name, I wont be voting for him on that basis, if there is a conservative alternative.
I see not much difference in voting for Democrat (D) vs. Republican (D) this year. But your mileage may very.
We debate this limitedlessly here on FR, but I doubt I would be convinced otherwise.
Best Freegards,