This is a Dear Colleague letter being circulated by Bruce Braley.
This is an interesting internal shift in the House, and suggests that no current ideological caucus is quite capturing the moment. The plank for this group is economic justice, universal health care, affordable college education, consumer safety, fair trade, and good paying jobs. Culturally, though, this has more of a rural farmer and union feel than the progressive caucus, with its heavily New Left and multi-ethnic approach, but policy-wise it is substantially different than the Blue Dogs.
The Blue Dogs are have always relied on the argument that their districts are more rural and swing than the mainstream of the Democratic Party, and positioned themselves as more populist than liberal. Since 2002, though, that group has become riddled with corporate lobbying influence, and their brand has suffered. The progressive caucus doesn't have any requirements for belonging, so it's stocked with anyone who wants to attach their name to progressivism for any reason, often so they can triangulate against progressives with something along the lines of 'even the liberal Barney Frank believes that a bailout of Wall Street is necessary' or so that Dennis Kucinich can use it as a stepping stone to run for President.
This is an interesting development, and I suspect there's going to be some strong caucus reorganization going on as an expanded Democratic majority finds its sea legs.