After reading Chris Hedges' excellent book Death of the Liberal Class, I had a better picture of the history of the "liberal" shift to the right. I think I would officially split the traditionally liberal side of the political spectrum into two groups:
1) Lesser Evil Liberals -- These are the Democrats who concede that Obama is the lesser of two evils but insist they will vote for him anyway, because they have a chance to win and "they're better than the Republicans."
2) Leftists -- These are former Democrats and third-partiers who will either not vote or vote for a third-party candidate, believing that you should vote for what you believe in.
I have found that this split has become almost as acrimonious and visible as that between Dems and Republicans. It gets bitter quickly. Some would argue that this is just what the right wing wants, a larger split on the left. But really, these two groups are fundmentally divided on tactical lines, if not in deeper ways. Incremental change versus radical change. Reform versus a system-shift. Change from within versus change from without.
If the non-Democrats rechristened themselves Leftists with a capital L, it could constitute the beginning of a third party movement that would support every leftward third party. It could be the start of a third-party coalition.