I like JD - but McCain is very entrenched. No better excuse for Term Limits than that guy.
No question. It's going to take somebody like JD to beat him.
I wonder, though, if McCain's status might be like the Soviet Union's in 1989. Everybody assumed it was forever...but, when some people who didn't know any better, started taking down the wall the whole edifice collapsed.
I don't read McCain as "popular" so much as he is viewed as "inevitable". That's how Hillary was viewed before the Democrat primary, remember. If somebody starts chipping away at that perception of inevitability, it could come apart rather quickly.
Ask yourself this: Who do I know that is really for John McCain?