I think the Clintonite's are vastly overstating their importance. Neil Sinhababu, who has a sustained argument about why Hillary should not be VP (which I recommend), notes that the cleavage in the Democratic party is vastly exaggerated.
[A]fter a Democratic convention where everybody in the party including Clinton talks up Obama and a couple months of campaigning against a warmongering GOP nominee with a 0% NARAL rating who doesn't care about working people, Obama will consolidate Democratic support.
We're moving through the stage in the process where there's maximal bitterness between the candidates' supporters. (I remember this from 2004, except it happened a lot earlier in the year.) But sure as Dean people fell behind the once-hated Kerry and people who care about each other make up after a fight, you'll see the vast majority of Clinton people cast a vote against McCain. And looking at the numbers, Hillary-Obama animosity is pretty tame by historical standards, with 1/5 of Obama people saying they won't vote for Hillary and 1/4 of Hillary people saying they won't vote for Obama. You know what percentage of McCain supporters said they wouldn't vote Bush in March 2000? 51%.
Indeed, I recall that many some were predicting that John McCain's challenge to George Bush would lose the Republicans the 2000 election. We all know how that turned out. John Sides, a political scientist, explains this effect of party members almost invariably rally around the nominee.
Despite ugly battles and policy differences that sometimes seem intractable, the reality is that presidential campaigns tend to unify each party behind its nominee. Political scientists call this phenomenon the "reinforcement effect." It was described in 1940 in the first major study of a presidential campaign. The study's authors -- Paul Lazarsfeld, Bernard Berelson and Hazel Gaudet -- noted that voters tended to "join the fold to which they belong," with Democrats gravitating to Franklin D. Roosevelt and Republicans to Wendell Willkie. These voters were not blindly following whichever shepherds their parties nominated, the study concluded. Rather, their partisan loyalties reflected their underlying values, and the parties' nominees solidified their support by emphasizing these same values as the campaign unfolded.
Obama has more to worry about than just Clinton voters. To keep the his base energized, Obama needs to maintain a clear anti-war message. Hillary Clinton suggest we "obliterate Iran", voted for the Lieberman/Kyl Amendment and voted to authorize the war we're currently in. It makes sense for Obama to try to court Reagan Democrats, but he should do so with a anti-war economic populist, such as John Edwards or Jim Webb.
A Obama/ Clinton ticket doesn't make sense from the standpoint of governing should the ticket win. I don't think we should see both Clintons and their cynical/ stupid advisors open up shop in the VP's office. Would they make use of the powers accumulated by the Cheney VP slot to undermine Obama? You can bet on it. This can't possibly be a good situation, and I can't see how it would last.
(Posted by Ewan)