We can’t be precise about how all of this will shake out. But it is reasonably clear that, to take back the House in 2012, Democrats would have to approximate the feat they pulled off in the banner year of 2006 while facing a changed and more hostile political map. Redistricting aside, a number of places where veteran Blue Dog Democrats lost in 2010—including three in Tennessee, two in Mississippi, and one each in Georgia, Florida, South Carolina, and Alabama—are heavily Republican districts that are very unlikely to flip back in the foreseeable future. The Senate picture for Democrats in...