As I say, there's lots to choose from in that GQ interview. At the top of my list is Penn's insistence that the campaign performed almost flawlessly till October:

Why couldn’t you bring your team this time?
I think this was organized in a way which, you know, some people think is a better organization—to have, instead of a team, almost a group of rivals. And you know, one would say, overall it worked pretty well. Till October.

What happened in October? How was that the turning point?
Well, October of ’07 we were forty points ahead. What happened in October, or really the beginning of November, was that Barack Obama personally attacked Hillary Clinton. Called her disingenuous. They attacked her in the debate on the driver’s licenses.

Ah, the driver’s licenses.
Right. And until then, basically, people were declaring the race over. The message strategy had been so successful that everybody was declaring it over. And they got so frustrated that what the Obama camp did was that they restrategized. And they concluded, obviously, the only thing they could do was attack her personally. It took us a while to kind of throw off those basic attacks. And I think that it was a tough organization to respond to that. You know, the response to a lot of those attacks became “Let’s do the soft, personal stuff.” And that didn’t work.

Go back to the licenses.
What happened was, Obama announced the day before [the debate] that he was gonna go after her personally. Called her disingenuous in The New York Times. Now, at that moment, and up until that moment, you know, we had won the experience primary; we won the new-ideas primary. A lot of the leads that we would rely upon in the big states were already built up. He was fading in the national polls, and he said, “Look, the strategy here isn’t working. I’ve gotta do something different.” And Obama did. He attacked her. And a lot of the press egged him on.

Hmm... How to put this? If you construct a campaign that succeeds marvelously up until the moment your opponent attacks, at which point the bottom falls out, then you haven't actually been succeeding. It just wasn't apparent until that point.*

The Maginot Line also worked brilliantly--up until the moment the Germans came streaming across Beglium.

*In fairness, I think what Penn is claiming here is that the campaign was going great until Obama attacked, at which point his colleagues dropped the ball. The implication is that the attacks wouldn't have been a very big deal if his colleagues were either semi-competent or had listened to him. But, again, the premise that it was all going great is, in retrospect, ridiculous. The appearance of success masked some serious vulnerabilities that just hadn't been explosed yet.

--Noam Scheiber