McCain was a very common sense republican - good on compromises and got things done. But he caved to their wing's extreme end and he got fucked.
When you think about it, so many GOP Veeps just had no gravitas. GHWB was very good--but the GOP turned on him because he was too commmon-sense.Jack Kemp was the Veep nominee in 1996--solid. But shit, they had Spiro Agnew, Dan Quayle (don't get me started on his douchebag son--he was too much, even for Arizona), Cheney, potentially Palin.
I don't even remember who Romney's VP nominee was. And remember Admiral Stockdale, who got tapped to run with Ross Perot? A great Navy man, but totally wrong for the #2 job.