David Ignatius of the Washington Post points out how McCain has compromised his own principles shaped by the military culture when he made the shotgun desperate decision to choose Sarah Palin as his running mate:
In the military culture that shaped John McCain, there is no more important responsibility than the promotion boards that select the right officers for top positions of command. It's a sacred trust in McCain's world, because people's lives are at stake.
[...]
McCain made the most important command decision of his life when he chose Sarah Palin as his vice presidential nominee. Two weeks later, it is still puzzling that he selected a person who, for all her admirable qualities, is not prepared by experience or interest to be commander in chief. No promotion board in history would have made such a decision.
The takeaway from all of this--as it's increasingly evident and clear that Palin is unfit to be one heartbeat away from being president--is that it's also increasingly clear McCain himself is unfit to be president.