Kerry 2008 would go really, really poorly for the Dems.
Have to disagree. A big part of the 2008 landslide was the feeling of realignment: Obama was sold as the ticket to a more progressive future free of the social backwardness, greedy excess, endless wars, and polarization many believed increasingly characteristic of the Reagan Era. The War on Terror and the Great Recession are still going to be the biggest issues in 2008. They're not going to be pinned entirely on the incumbent, who presumably won in the first place because of discontent with Bush, and his failure to solve those issues isn't going to make a majority run back to a platform they feel failed. Turnout would just be low. That's not to say Kerry wins or does well, obviously, but it's not the blowout that Obama vs. McCain was.
It's more like if Reagan won in 1976 then lost in 1980: the zeitgeist is still in the Republicans' favor, or in the case of Kerry '04, the Democrats'.