The line thrown by Walter Mondale at Gary Hart during his comeback in the 1984 presidential race was echoed in recent days, supposedly coming from Hillarians at Obama. This shows their filling the same roles from that era: Hillary as Establishment Dem and Obama as New Centrist Dem. The third role is Leftist Insurgent, now being played by Edwards, with Jesse Jackson playing it in 1984, after George McGovern dropped out. These roles frequently pop up in races for the Dem nomination for president, and I think can be traced back to at least 1960.
Labor's role in this has changed. They used to always be part of the Establishment candidate's support. But, ending of the Cold War, more youth in labor, and greater inequality, have pushed labor left, with it now split itself and also among the candidates. Another oddity is that the Clintons collectively have played in all three roles: supporters of a leftist insurgent with McGovern in 1972, Bill the New Centrist in 1992, and now Hillary as the Establishment candidate.