In '08 or '12, I suspect--and that's what I think Penn is driving at here (italics mine): 

Looking at the big picture down the road, years from now, how do you think history will view this campaign?

Well, they’re always going to look at it and say, “Well, it was a surprise that she didn’t win.” And they’ll look at her and say, “She was the first woman that had a real opportunity.” Look, we never know what’s gonna happen later on. A lot of people have come back. It’s pretty unusual for somebody to win the nomination the first time out.

Update: Alex Massie writes in with a good catch: Is it really so unusual to win the nomination on the first try? Not for George W. Bush, John Kerry, Bill Clinton, Michael Dukakis, Jimmy Carter, or Walter Mondale. And, of course, Barack Obama. Recently it's been the norm, not the exception. (Thanks to commenters for adding more. Also, as they note, for some reason it's recently been easier for Democratic first-timers than Republican ones.)

--Michael Crowley