Re Michael’s earlier post, pollster Glen Bolger has a slightly different take. Not contra anti-incumbenecy, but in tandem with it, he writes that the likes of Specter, Lincoln and Crist are victims of hyper-partisanship:
The nomination defeats (or major troubles at this point for Lincoln), are politicians who were punished for their votes and efforts that strayed from the party line.
…
Not every incumbent is endangered for renomination. However, those who face anger from the grassroots, coupled with a challenger candidate with the resources to get their message out, have challenges.
Marc Ambinder nods in agreement, adding:
Proximity to congressional leadership seems to be triggering primary challenges early, as local activists resent the top-down imposition of a candidate. In the case of Harry Reid, it is his status as a leader himself.