The reasons for an Obama/Clinton ticket are quite strong - both have dedicated and passionate supporters; the "dream ticket" would heal the divisions within the Democratic Party more quickly [though the nuts at Hillaryis44, still stuck with the image of '90s Hillary Clinton, may never be appeased, more rational folks should get on board.] And Senator McCain is unlikely to have a VP as strong as Senator Clinton - Condoleezza Rice would reinforce the "Bush-3" perception; Senator Clinton would shred anybody else (though Alaska Governor Sarah Palin may be a respectable adversary with a strong ethics/reform platform). Effectively, Senator McCain would be running against two opponents.
Of course, there are problems - Senator Clinton's own remarks are already being used in GOP ads; some Independents as well as some Democrats may vote against a Bush-Clinton-Bush-Clinton train. I consider the first the more serious problem.
So a question is - if not Senator Clinton, then who? Any woman VP would be seen as a "not-Hillary" attempt at wooing women voters. So there has to be good reason to choose a woman VP. I thought Kansas Governor Kathleen Sibelius would be a good choice - but Kansas may be too red. On the other hand - two-term Arizona Governor Janet Napolitano? Of course, Senator McCain's from Arizona as well. But that's precisely the point - the sheer audacity of the pick would show that the Democrats are taking the fight to Senator McCain's homeground. With Arizonians on both major party tickets, there's less of a "favorite progeny" factor. Senator McCain would have to spend time and money defending a "given" state, further stretching his resources (considerably lower, for sure, than Senator Obama's). And IMHO, that's a good compelling reason to have a Democratic VP pick who happens to be a woman not named Clinton.
Coda: Here are some interesting reads, all via RCP:
Amy Sullivan at Time says Senator Clinton's candidacy (likely) failed because she did not win over 60% of the female vote. The over-65 crowd voted overwhelmingly for Senator Clinton; younger women went for Senator Obama; but the tie-breaker, middle-aged women, split evenly. She describes "optimist feminists" and "pessimist feminists" - the former not having to prove anything to others (a la Senator Amy Klobuchar), while the latter still feel sexism is all-pervasive, and figure that if Geraldine Ferraro ran in 1984 and Senator Clinton in 2008, the next serious female candidate will take another full generation. Senator Klobuchar backed Senator Obama.
Peggy Noonan, formerly a speech-writer for President Reagan and currently a columnist at WSJ, says Senator Clinton "lacked the grace to congratulate the victor" in her Tuesday night speech following the last primaries. Noonan also says America "dodged a bullet" by not having to put a Clinton back in the White House, as "Mrs. Clinton would have been a disaster as president... Mr Obama may lie, and Mr McCain may lie, but she would lie." Etc.
Hendrik Hertzberg of The New Yorker was at Baruch College during the afore-mentioned Tuesday night speech, and says in that setting, the speech did not come off as badly as some bloggers and commentators have made it out to be. He writes:
"I’m sure that this speech looked confrontational and intransigent on television in ways that it just didn’t in the hall, inside the bubble. In the hall, you don’t see the speaker in closeup. You see her in the distance, in the midst of a crowd. The effect is communal, not egotistic. There are no replays of selected highlights, no panels of experts. You’re left with a mood, and the mood was calm.
So I felt a certain relief, as did other Obama supporters in the room with whom I spoke."
But he also points out that on later reflection, Senator Clinton's congratulatory words for Senator Obama could just as well have been said by the victor for the loser, even though Senator Obama had won the primary race. He also does some math (in hindsight) that shows Senator Clinton was conflating the popular vote tally to give the appearance that she had won far more popular votes than Senator Obama; at best, Hertzberg says, the popular vote race is a tie.
Finally, Clinton advisor Gene Sperling says Senator McCain is the "Master Economic Flip-Flopper."
[I must admit I did not watch Senator Clinton's speech; I was out grocery-shopping and barely made it for Senator Obama's speech.]