Let me draw up a scenario for you. You're a long-term incumbent Republican in a purple state that may or may not be trending blue. You've always been a moderate and coasted to easy elections in the general. However, a bunch of rabble-rousing conservatives and tea partiers, the kind of people you never liked anyway, have propped up some firebrand conservative candidate, and the polling seems to indicate that you'd have trouble winning a primary election. In your own party. The unkempt, church-going rubes; you never really liked them anyway.
You're approached at the same time by the then-wildly-popular Democrat President who carried your state handily, and your State's Democrat governor, who has a fabled turnout machine. These two guys promise you that if you jump ship and switch parties, they'll throw you their support. Sure, there's already a Democrat in the race, but they promise you every bit of their formidable monetary and establishment power. The President assures you that he'll offer this upstart Democrat a position as a diplomat or cabinet undersecretary or something, and you'll coast to a primary victory. Then, since you'll be the nominee of the state's preferred party anyway, the general election will be a breeze.
Sure sounds better than trying to mollify those icky tea partiers for two years, doesn't it? A little easier to swallow? Sounds like a safer route to travel, to boot?
I've got news for you, buddy. It's not going to shake out that way. And let this be a memo to other milquetoast establishment figures who might someday find a popular conservative daring to challenge them in a primary: Don't believe the media hype about the Republican party moderate purge. Despite the fact that they're going to get shellacked in November, the Democrats are even more pissed about their moderates than we are. And if the combined power of Obama and Rendell can't save you from the teeming horde of orange-clad hippies, no one can. You've got exactly one chance to survive, and that's to stay in the party that's funded your re-election year after year, go home to your state, and convince the Republican residents thereof that you deserve to keep representing them year after year, as the best chance for compromise they've got.
Maybe they'll buy it, maybe they won't.
But what we learned last night is that bolting to the Democrats will bring sure and swift destruction - and no matter what Obama says, he cannot save you.