Here's a slightly counterintuitive angle on Rep. Parker Griffith's party switch: his switch to the GOP could actually become a problem for the GOP, in that his reelection race will spark some jockeying on the right over whether or not to support him.
Griffith will be welcomed by the GOP--it's been reported that he was courted by Republicans, and that the National Republican Congressional Committee scrubbed its website and YouTube of attacks (like this one) on the former Democrat--but The Washington Independent's David Weigel notes that conservatives don't like him: RedState's Erick Erickson proclaimed, "We can pick this guy off and get a real Republican in that seat," and the Club for Growth--known to back primary attacks on moderate Republicans--doesn't sound too hot on Congress's newwest Republican either, noting that Griffith voted against President Obama's budget, stimulus, cap-and-trade, and health care initiatives, but that he voted against amendments that would decrease the size of the stimulus.
And Griffith's Republican challenger, Madison County Commissioner Mo Brooks, will still run in 2010, this time as a primary opponent. Brooks was at a severe cash disadvantage to Griffith in his October quarterly finance report, with $113,000 to Griffith's $618,000 in his campaign war chest, but Brooks announced his candidacy over the summer--meaning he's not doing all that badly compared to an incumbent.
A Democratic defection is, to be sure, good publicity for Republicans...but it's not quite as good if conservatives turn around and back a primary challenge off the bat.