Newsweek has done a post mortem labelling the McCain campaign effort among the worst in recent history, even comparing it to McGovern/Eagleton
http://www.newsweek.com/id/167561
The reasons were primarly as per Newsweek a) Palin and b) McCain's failure to be optimistic.
Now I think this is nonsense, pretty much. Had McCain chosen a bland, experienced running mate GOP turnout would have been even more dismal, probably ending another dozen house careers and 2-3 senate careers. And running "morning in America" in the face of a single digit "right track" number would have been mocked as painfully out of touch and clueless.
But there's a bigger problem with this thesis. McCain's effort was only mildly subpar compared to its "peer group"
Since 1960, the following candidate have tried to get a third consecutive term for their party.
1960; Nixon 49.5%
1968 Humphrey 42.7% (third party in double digits)
1976 Ford 48%
1988 Bush 41 53.4%
2000 Gore 48.4%
http://uselectionatlas.org/RESULTS/
McCain ran slighly behind the number that Nixon, Ford and Gore had; all of whom were running in better economic times than this year. He ran ahead of Humphrey, who was saddled with fallout from a far more unpopular war than Iraq, but due to the weird quirks of 1968, nearly won the popular vote and nearly forced the election into the House. The only candidate of the bunch that stands out is Bush 41, who ran under times of peace and prosperity; had the brilliant Lee Atwater running the campaign; and faced a very weak opponent.
The proximate cause of McCain's defeat was , in my opinion, the Wall Street bailout. In specifics, once he made the call to suspend the campaign he needed--barring such immovable objects as scheduled debates--to get the issue off the burner as soon as possible.
On September 29, McCain left Washington for a rally with Palin in Columbus OH. Now he was going back to OH plenty more---what he needed to do was beg, borrow and plead with House Republicans to pass the bailout bill that afternoon so he could declare the crisis resolved and get back on the campaign trail without having this hang over him. I have no diea if haunting the Capitol building would have squeezed out enough votes--I just know the bill failed in the House, keeping the crisis at full boil for another precious campaign week. http://blogs.wsj.com/washwire/2008/09/29/ (Yes, the bailout was a "crap sandwich"; but McCain had already endorsed getting one passed; the ship had sailed as far as coming out against it)
September 29, 2008 was the day John McCain's best chance to become President slipped away. This was one political event that should have been left to Governor Palin to handle solo. Having gone "maverick" and back to DC, switching gears to go back on the campaign moved to be a tragic miscalculation for McCain.
The Newsweek article does point out McCain's inability to stay on message as far as policy differences between Obama and McCain. That observation isn;t very novel and when I sit down and catalog the myriad Mac errors, that will be among them.