I've been doing a quick study on National Journal scores, vis a vis the comment that whomever the Dems put up is the "most liberal." And in fact it's true...

Kerry WAS the most liberal senator in 2003.

But there's a simple explanation for this. When a Dem knows he's going to run for president, he needs to get the kook, left-wing base on board in the primaries. So he has to tack left.