Why did the media snow job work on Bush but isn't working for Obama?

In hearing some stats about Obama's approval numbers (which are getting pretty darn low), a thought occurred to me.  Things may not have been perfect under Bush, but the media managed to convince many Americans, including many normally very thoughtful and intelligent Americans, that Bush was the worst President in history, even though there was little, if any, data to support this.  This snow job helped Obama get elected.  Now Obama is in office and the media has mostly been trying their hardest to keep public opinion of him high (although there have been some defectors more recently), but the snow job doesn't seem to be working this time.  You could say that people can just look out the window and see how bad things are, but I would say again that things were not all that bad (relative to today or other bad times in history) when Bush was President and the media still succeeded in convincing people that times were terrible.  Why is it not working this time?