In order of likelihood IMO:
5. Runs again, loses primary, runs as independent a la Murkowski and then all hell breaks loose.
I think this might be the most likely option actually. Don't know why you have it at 5th. McCain is certainly no Bob Dole, no Romney, no Lieberman, no Sarah Palin for sure and neither no Paul Ryan. Basically, McCain might very well have been the most sympathetic Republican candidate on a GOP ticket since the good old Eisenhower. Okey, so he wants the US engaged with the world, but that doesn't automatically make him a bad guy in my view. And right, he was damn wrong on Iraq, but so was Hillary and almost everyone else. Give him a break. At least he's not Reagan! Or Cheney! Or W! Or giving tax breaks away like crazy as Romney for sure would have! Better with a military semi-loon (although he really isn't and never has been, in my view he's actually if anything to the slight left of Hillary) than a tax break loon like freaking Romney for God's sake! Romney would have meant the end of the US as we know it - Romney would have meant that the US would simply have become an underaffiliate of China Incorporated. With all his rhetorical talk about hating China, what Romney really wanted was to give Halliburton and Dick Cheney even more power to become Chinese, or Russian for that matter.
Poll
