David, I have some tentative answers for you (and some questions of my own). There are three explanations, I think, for Clinton’s cancellation–and all of them paint Clinton as rather juvenile. They fall under the rubrics of temper, sensitivity, and, of course, partisanship.
Temper: she was irritated by the fact that she was not informed that Palin was also coming. The reaction of her spokesperson seems to express such anger–and by the way, I do think that’s a reasonable annoyance, but of the kind worthy of a shouting match, not a cancellation. Conclusion: personal pride is more significant to Clinton than the threat of Iran.
Sensitivity: Clinton just can’t stand the idea that she’s no longer the biggest star of every event she might be attending. This will become more problematic when the memory of her candidacy fades away and the new people in power get most of the attention (she will only be saved by an Obama electoral defeat). Conclusion: Clinton’s celebrity status is more important than the threat of Iran.
Partisanship: Clinton thinks Palin is so terrible, such a disaster for the country, that she will not even appear with her on the same stage, no matter what the cause might be. Conclusion: snobbishly shunning Palin is more important for Clinton than stopping Iran.
A few more points on this:
1. The battle against nuclear Iran is supposedly bipartisan. The parties might differ in tone and policy, but they both agree that calling for the elimination of Israel is not something to be taken lightly.
2. Just a week ago, Obama and McCain had no problem appearing on one stage (in NY, in 9/11) when the cause seemed to justify it.
3. Palin is a VP candidate, whether Clinton likes it or not. The organizers of such rally can’t be expected not to invite her, and not to be happy if she accepts the invitation.
4. This will not go down well with the more hawkish Jewish voters.
5. I suspect it will also be problematic with some women voters (where’s the sisterhood of the traveling pantsuits all gone?).
And now the questions:
1. Will Obama pick up the tab and send Joe Biden to the rally?
2. Can he do that without making Clinton even angrier?