Nate Silver gives horse race junkies a 2010 preview:
Many of the voters who went to the polls in 2008 did so because of Barack Obama; almost 90 percent of those voters also happened to vote Democratic for Congress. But many of those voters will not turn out next year without a presidential race to pique their interest. Some of the same Democratic representatives who most benefited from Obama’s coattails in 2008, then, are also the most vulnerable to an upset. Their fate may depend on how much this president can personalize that election and, of course, how much he can mobilize his powerful voter-turnout operation for them and how well liked he can remain. Obama’s popularity is the Democrats’ greatest asset heading into the midterm elections in 2010 but it is also in some sense their greatest liability.