Hans Noel makes a very good point:
The modern progressive movement also has no qualms about criticizing Democrats for too much compromise. Obama has almost as many critics from the left as from the right, notably on Obamacare (too watered down) and foreign policy (unmanned drones). But liberals/progressives/the left do not take ownership of the Democratic Party. They seem to recognize that the Democratic Party is the party that they should like, but they put the onus on the party to come to them. Its the Democrats’ fault because they have no spine. The Tea Party never lamented that the Republicans didn’t have a backbone. The Tea Party decided it was the party’s backbone. The Tea Party didn’t wait for the Republicans to come to them. They put a rope around the party and pulled.
If you are disappointed with the direction the Democratic Party is going, and you want to push things in a more left wing direction, then you need to get more active, not less.
Disappointed that Obama hasn’t gotten more done? Work for a Congressional candidate or a Senate candidate who’s closer to your values. Support left wing primary challengers. In every primary and general election, knock doors, make calls and give money to the more left wing candidate.
There’s no other way to do it. No quick fix. The right wing political base understands this. When they get disappointed, they get active. They don’t throw themselves a pity party and whine about how they’re going to sit out the election. That’s not how you win.