What is the significance of Democratic Congressman Parker Griffith's switch to the Republican party? The liberal line is that Griffith already voted with Republicans so he was just making it official. The conservative line is that it portends the coming tide of Democratic losses and party-switches in conservative districts. But Matthew Yglesias, never much one for accepting the standard partisan spin, explains why it matters in a way that accounts for both arguments.

I think this is a reminder that the Democrats’ current huge majority with 257 members isn’t remotely sustainable. To get a majority that big you need to win a lot of districts you just can’t reliable win. Substantial losses in 2010 and/or 2012 are basically inevitable. That said, there are still a few GOP-held House seats that could plausibly be won by a reliably liberal Democrat. The real issue is whether the Democratic majority can add a few seats like that, and contain losses enough to maintain 220-230 reasonably reliable votes and thus the effective ability to govern.
Yglesias concedes, "The practical implications of this seem to be basically nil." But he goes far beyond the short-term meaning of one Congressman to look at what this could mean for the Congress as a whole. His analysis is not particularly flashy or sensational, but it's exactly the kind of reliably thoughtful analysis that explains Yglesias influence and makes him one of the few bloggers to be in the Atlantic 50.