If Clinton or Carter endorsed a Republican I think that most people might have to stop and find out why. If they were able to give articulate, reasoned arguments for that choice then anyone with half a brain would have to think about whether their own choice was being made purely as a result of holding the party line.

Powell gave some very good reasons for his endorsement of Obama, none of which had anything to do with race at all. They had to do with his own opinion as to who would make the best president of the USA. To my mind that was a very patriotic thing to do - he is going against the party he has been aligned with, probably at some risk to his own possible future prospects, in order to do what he sees as best for his country.