Excellent reporting from Aaron Blake, who notices that all seven of the candidates that Bill Clinton has endorsed in Democratic primaries this year supported Hillary Clinton in 2008, while in six cases their opponents endorsed Barack Obama.
Blake ends the piece by framing it around the question of how important Clinton's endorsement might be, but what I find far more interesting is whether we're seeing the beginnings of a more enduring factional split or not. I've done some research (with Casey Dominguez) that sort of touches on questions of factions within the Democratic Party, using data from way back in 2000...we were interested then, among other things, whether DLC involvement was relevant to the Gore/Bradley choice. The whole question of party faction, however, is still a fairly obscure one as far as I know, especially in the US context (explicit, well-organized factions have been important in some other democracies, but they don't really happen here). So the question I'd have is: could something that begins essentially as a personal faction in presidential politics wind up getting institutionalized and spread to state and local politics? If so, would it eventually develop policy components -- even though the original split didn't really have any?
My guess is that the answers to these questions is that on a theoretical level, this could happen. But in the present Democratic Party, it's very unlikely. Both of those, however, are just guesses...anyway, if you want to know what I find really interesting, it's this sort of thing. I'll almost certainly be looking out for it when the 2016 invisible primary gets underway (which, of course, isn't all that long from now).
Oh, and: great catch!