Personally, I think McCain has potential. Unlike Kerry or Hillary, he doesn't change his stated position based on the crowd he's in front of, but based on sensible principles (e.g. not drilling offshore makes sense when oil is cheap and the tech is dirty, but not now when gas is expensive and we can get the oil without harming the environment).That's the kind of "flip flop" that's a good thing.
However you justify a flip flop is up to you. If you were inclined to like Obama more, then you would probably agree that his flip flopping on the issue of public financing for his campaign is fine. Here, you see McCain's flip flop on offshore drilling as timely and commonsensical, but you probably more inclined to think so because you want to. Obama supporters will probably say that his flip flop on campaign funding is because it is commonsensical in trying to win the Presidency and therefore fully justified.
Frankly, it's still a flip flop (for both of them). I don't care what issue it is, but politicians always flip flop while running for office. Even more so when running for the Presidency. It isn't
what issue they flip flop on, it is
when they do it that matters.
McCain is trying to appeal to the republican base and, I believe, in doing so he is alienating a lot of independent voters who respect(ed) him for his maverick streak. I count myself in that category. For me, McCain went into election mode back when he made amends with Jerry Falwell. You don't call someone an "agent of intolerance" and then make amends with them
when running for President. And yes, I am referring way back to his run in 2000 when he denounced the extreme religious right (here, I took the time to find a
video).
One last thing, why did you mention Hillary and Kerry when Obama is the nominee? I understand you may have a historical dislike of certain nominees, but not everyone is the same as those who have come before. If that were true then we would refer to all republicans as Nixon.