Mark Penn's arguments are so weak that they practically count as an argument for the contrary. This is a particularly frustrating talking point:
No one believes that if Hillary had been president she would have started the war.Yes, but this is a completely irrelevant hypothetical. Hillary did opt to support that war, and voted for it. She wouldn't have come up with the idea on her own, but that doesn't make her judgment any better. It's worth noting that many Democrats (wrongly) trusted her and her husband's judgment on on this issue.
Jon Chait is just as frustrated as I am with arguments that we can never really tell how electable a candidate will be. The post well is worth reading, and is a good antidote if you are taken in by Mark Penn.
That so many Democrats think this question is complicated suggests to me that maybe people aren't good at assessing the popularity of their co-partisans. To Democrats, it's perfectly obvious that the strongest Republican nominee is John McCain. He polls very highly, everybody knows Democrats and Independents who like him, and so on. But Republicans are constantly debating this. You see Republicans spinning horror scenarios of a McCain nomination leading to a splintering base or depressed turnout. To Democrats it's bewildering that they even debate this. Lots of Republicans feel the same way about the Clinton/Obama electability debate.In these arguments, those don't want to concede that Obama is a superior general election candidate inevitably say "this is the kind of logic that led to ...John Kerry." I think it's time to put that Kerry boogey-man to rest. Just because people sometimes get the electability question catastrophically wrong does not mean that we cannot make educated predictions about the subject.