There's a lot of interesting stuff in this John Dickerson article on what last night's results really mean, but this last paragraph is probably the one that needs to be most referenced:
The night showed just how limited Obama's political power is. He said he'd work all-out for Specter, but he didn't campaign for the senator in the final days. That may have been a wise reservation of his political capital (he's already been ineffective in previous races), but it also demonstrated how much has changed since 2008, when Obama was talked about as a force that could remake the political landscape. Critz won by running away from Obama's signature achievement, and Lincoln, whom he supported, was forced into a runoff. For a president who is still far more popular than the Democratic Congress he aims to help, yet who is unable to translate much of that popularity to do so, this condition may be best described as limbo.
Assuming that 'Limbo' is a synonym for 'orbital decay.' The problem for the Democrats is that they do not have several hundred Mark Critzes out there running for Congress, all secure in the knowledge that they didn't vote for the 'stimulus,' didn't vote for cap-and-trade, and didn't vote for health care rationing. Instead, they have several hundred variants of Joe Sestak (who voted for all three), Frank Kratovil (who voted for two out of three), or Glenn Nye (who voted for just one of three). And all of those Democrats were promised, in exchange for their support of some fairly drastically unpopular legislation... the President's intervention in the 2010 election.
Crossposted to Moe Lane.