Like Kevin, I'm not terribly concerned about the divisiveness of the primary. Not only don't I think it terribly divisive, but I certainly don't believe that Clinton's folks are coming up with anything that McCain's oppo researchers will miss. By presenting it in a slightly softer form during the primary, Clinton's attacks may actually act as antibodies for Obama, helping him to formulate responses and making the media believe this ground has already been hashed over. As for the literature on whether divisiveness hurts, John Sides writes, "Perhaps the most relevant study is by Lonna Rae Atkeson (here, gated). She examines presidential elections from 1936-1996 and finds that the relative divisiveness of the two parties primaries is not related to the general election outcome, once other factors, namely the state of the economy and the popularity of the incumbent president, are taken into account." That shouldn't be too shocking. Most primaries have a presumptive nominee, either a VP or an incumbent. They're only seriously opposed when they look weak, so it makes sense that a lot of incumbents who are opposed end up losing. But the causality doesn't run from the primary challenge to the loss -- rather, it's the likely loss that sparks the primary challenge. If you look at 1968, for instance, Johnson should've been the presumptive nominee, but his weakness on Vietnam led to intra-party challengers, leading him to drop out. It was the circumstances of the moment that led to the challenges, and the rifts in the party. Similarly, in 1976, Reagan opposed Ford because Ford was near to Watergate and thus a weakened candidate. Strong candidates scare off primary challenges and win general elections. Weak candidates attract primary challengers and lose general elections. Clinton and Obama are in rather different shape. It's the strength of the two candidates that's continuing the contest, and the party doesn't disagree on anything fundamental. There are real dangers if it splits over who is eventually chosen -- a particularly likely outcome in the case of convention shenanigans -- but there's nothing intrinsic to a long primary battle that harms the party.
