Progressive is in many ways just the new label for what used to be called liberal before, say, the Clinton administration. The liberal label over time evolved (at least in some circles) to apply only to the more suburban white well-to-do part of the Democratic base – not particularly union-friendly, not particularly concerned about the social safety net, interested in looking environmentally-conscious without having to change their lifestyle, and so sad about racial injustice that they hope very fervently that somebody else will finally do something about it before they have to sit through another depressing movie about it.

Progressive identity arose the way lots of identities do – simply as a means of saying “I’m not one of them!”