I don't remember Bush being popular in 2004.
Actually, when you think about it, it's amazing how similar the 2008 race is to the 2004 race. We have a formidable establishment candidate who originally backed the war, then changed his mind (John Kerry then, Hillary Clinton now); a challenger who has opposed the war all along, and who is clearly out of his depth (Howard Dean, Barack Obama); and a third guy who stands around looking pretty (John Edwards, John Edwards). The biggest difference is that Mike Gravel doesn't quite have the gravitas of a Carol Moseley Braun.
This year, of course, everyone seems to think the Democrats are very likely, even guaranteed, to win. That's because, unlike in 2004, George W. Bush is very, very unpopular. The biggest danger for the Dems, then, is that their nominee will figure out that Bush is not on the ballot and won't know what to do.