But as you point out they can and have spoiled. I think many of them have reached the conclusion that centrist Democrats have a "like it or leave" attitude. If centrist Democrats can't find a way to work with the progressives we must face continued electoral losses.

As you point out, centrists outnumber the more left leaning side. Looking at it from the left side, it seems like the centrist Democrats enter all negotiations by leaving out all the lefts positions. That is a negotiate from the center to the right stance. I imagine it's pretty hard for a left leaning person to argue that the Democratic party has any progressive wing from that perspective.

I'm not arguing that the left doesn't need to compromise, but I am arguing that the center should look at how they act and decide if their position is "compromise" or "submit."