Lincoln faced a challenge from the Lt. Gov., Bill Halter who was heavily supported by unions and other out of state interests for her opposition to the public option. I was suspicious of Halter for his championing of a state lottery, the beneficial proceeds of which go to college scholarships. A Lincoln's campaign operative called to ask about how I intended to vote in the primaries back just after the Medicare vote. I told them I was very disturbed by her position on the public option but that if she took on the financial industry and was effective I would probably vote for her. She did and I did. Not a cause and effect relationship, but she probably got similar results from other more left leaning constituents.
Be glad if you have genuine progressives that you have the privilege of supporting. The best I can hope for is that some of my moderates might do the right thing on important votes on important issues. As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."