In assessing a potential unity ticket, Mark Schmitt says:
Obama is in many ways the most plain-spoken liberal to win the Democratic nomination since Walter Mondale. But while Clinton is probably inherently more cautious than Obama, her record marks her as more conservative on only one issue, and that's the one on which she is most out of step with the vast majority of Americans--the decision to go to war in Iraq. And yet, she still suffers under the reputation, developed during the 1990s, that she is some sort of quasi-socialist. That's the worst possible combination: perceived as more liberal than she actually is, while being demonstrably more conservative only on less popular points.
Yglesias, in addition, notes the craziness of adding Clinton to the ticket for foreign policy "cred." It's just bizarre that there are still Democrats who seem to think that taking a politically and substantively disastrous position on the most important issue of the Bush era is some kind of asset. At any rate, since I think these arguments were the best ones against Clinton's candidacy for the top of the ticket, it's not surprising I also think they're good ones against making her veep. Support for the Iraq War should be a disqualifying factor or something close to it.
There is, I think, and important larger point here. Some people have talked about this week's primary as being salutary because Clinton's silly gas tax pander failed, but that's a trivial example. The war is the big one. Admittedly, this is the kind of counterfactual that's impossible to prove, but my guess is that if she had voted against the war Clinton would be the Democratic candidate. Given the closeness of the race, her inherent advantages going in, and that the war had to be a liability it's hard to imagine that she wouldn't have prevailed without the Iraq albatross. Whether or not Clinton's support was sincere -- I don't think it really matters -- sometimes getting big policies wrong really is politically damaging. (See also the 2006 midterms.) This is evidently a good thing.