[Verginius Rufus]

I can see two scenarios where Hillary would win--a weak Republican nominee, or a strong third-party candidate drawing more votes from the Republicans than from the Democrats (like Perot did).

I'd like to think she'd be a sure loser, but four years is a long time to look ahead in politics (who in 1972 thought that the 1976 race would be between Gerald Ford and Jimmy Carter?). About 2007 if it looks like Hillary can't be stopped from getting the nomination but is likely to lose the election we might see a lot of panic on the Democrat side...they would be looking at another 4 or 8 years in the wilderness.

[ctdonath2]

or a strong third-party candidate

Bingo! Start watching for a suspiciously funded right-leaning third-party candidate. There's her winning strategy, both siphoning off opposition votes and creating a distraction.