HOW TO GET REAL. Mike Crowley notes some irony in Arianna Huffington lecturing Joe Lieberman on what "real Democrats" do seeing as Huffington was a Republican through the bulk of the nineties and a "pox on both houses" radical circa the turn of the millennium. I think there's maybe a broader point in this vicinity.
Just about ten years ago, the big issue in American politics was "welfare" -- Aid to Families With Dependent Children. That issue was eventually resolved in a deal between Bill Clinton and Newt Gingrich that many liberals regarded as a sellout of core principles and many conservatives regarded as a sellout of Bob Dole's presidential campaign. Today, politics doesn't work like that at all either in terms of the substance of what was considered important or the process by which all that happened.
Simultaneously, a lot of people have rather quickly risen to at least moderate levels of prominence within progressive politics who weren't really involved back then. Sometimes (as in the case of Huffington or, say, David Brock) that's because they were conservatives, more often they just weren't nearly as engaged as they are now. People whose primary point of reference is very recent American politics (I would include myself here) naturally have somewhat different ideas about what it's all about and What Is To Be Done than do people who cut their teeth under a different prevailing paradigm. Lieberman, meanwhile, is truly an outlier in terms of not having adjusted his approach during the Bush era. To people who've been doing this for years, it seems very strange to have all sorts of people who nobody had heard of seven years ago (or people who were actually Republicans) show up and try to lay down the law, while others of us find it very odd to watch people struggling to shake off the cobwebs of 1990s-vintage politics at a time of dramatically altered circumstances.