Josh Marshall has the right idea. Well funded primary challengers to right wing Democrats will beat them, even if they don't eventually win elected office. There are some issues about which I understand how geography dictates certain positions. Social Security is not one of them. And, frankly, who gives a shit if we lose a couple more seats.
The social security issue comes down to this: The Democrats should be able not only to beat the Republicans on this, but also to beat them over the heads with it. It needs to be the cornerstone of the identity of the Democratic party.
Without debating the wisdom of any of these things, I want to point out that the Democrats have been running from or are in the process of running from their core positions on: gay rights, gun control, welfare, trade policy, affirmative action, reproductive rights, church/state separation, public education, progressive taxation, etc... etc... etc...
While policies are not ideology, they are the real world manifestation of it. If there is one issue which the Democrats should be able to claim loudly and proudly as their own, without apologies, it's social security. If they can't figure out how to do that, and to get their members in line, then they really will have lost.
I overheard someone in a restaurant the other day saying something along the lines of "Bush captured the center by running to the Right." I'm not be sure how true this is, but the idea was that by running to the Right, Bush proved he stood for "something" and voters approve of that, even if they don't approve of the policies themselves. I don't know how much this matters, but I do know a party has to stand for something.