In the long run, the Republicans are hurting themselves with all this infighting. If they smear each other too much there'll be no one left who looks right for the Presidency by the time the nomination is dished out, and then they're out of luck.
I only caught a little of the debate the other night, but it looked like the Democrats were doing more to keep things light and were mostly attempting to avoid launching direct attacks against each other (except for Edwards' remarks toward Clinton). With the exception of Hillary Clinton, the Dems mostly look like they don't mind the idea of working together (think cabinet positions for those who don't get the nomination - Shaman's idea that Biden might be looking for that more than the actual presidential nomination might not be far off), whereas the Republicans are ripping each other apart.
I think they're hurting themselves a lot with that kind of thing. Anyone else?