Democrats are raising the bar to evaluate the election results

Democrats are claiming that they should face a loss of 45 seats in the House based on regression using the president's party, how many seats that the president's party holds, and personal income growth. Jonathan Chait adds five to ten more seats to that total in what seems like double counting (he says that Obama's election swept in some Democrats from Republican districts when the variable for the number of seats that the president's party holds already accounts for that ("the more seats you hold, the deeper into hostile territory you're stretched, and the easier it is to lose seats")). My guess is that if Democrats were asked about this a few months ago, they would have picked a much lower number. They want to raise the number so that they don't look to bad after the election.