Playing with numbers...
The Mainstream medias assault on Sarah Palin cost the Republican party 2.5 million voters who switched, for a 5 million vote swing.
John McCain was portrayed as too old even though his 96 year old mother accompanied McCain on the campaign trail and could kick the butt of many of the pundits who said John McCain was too old. Loss of another 2.5 million voters for another 5 million voter swing.
Barack Obama accepting over 200 million dollars in undocumented donations, another 2.5 million voters affected, for another 5 million vote swing.
The media used the above results to create an illusion that it was McCain who was desperate, another 2.5 million voters lost, another 5 million vote swing.
Bill and Hillary Clinton encouraging voters to vote for Barack Obama, another 2.5 million voters, for a swing of 5 million.
In terms of raw numbers it would be too simplistic to say that the above total cost John McCain 25 million votes. It is likely that more than one of the above affected the same voter. So even though there was a potential 25 million vote swing, I would say that average voter probably was affected by 3 of the 5 big reasons given above. So subtracting 15 million from the above we get a potential 10 million swing in voters if none of the big five had happened up above.
This years race would have been a virtual tie if Bill and Hillary Clinton had not been involved, and if Bill and Hillary Clinton had jumped ship over to McCain's side, they might have made enough of a difference to swing the race to John McCain, although they would have create a scenario in which both sides of the political landscape at one time either loved them, or hated them.
I wonder how many will respect the Clintons.