Here's another way of thinking about the question of voting for Dems even when they act spineless, as they did in the "Torture is Great, Habeas Corpus is Bad!" debate.
Q. Are all Democratic Representatives and Senators spineless?
A. No. There are plenty of examples of strong leaders in the party. They just represent the minority at this point in time. That's why we need to elect even more strong, progressive leaders so that they can swing the caucus into action instead of following the old tried and true "keep our powder dry" strategy.
Q. Do you live in a District/State with a strong progressive Dem (either as an incumbent or an up-n-coming challenger)?
A. Great! You are the envy of other Dems who are not so lucky. You should do whatever you can to help get them (re-)elected.
Q. Do we want what few strong progressive leaders we have to have even more power?
A. Of course we do. Which is why increasing their numbers is vital.
Q. Is there another way we can increase their power?
A. Yes! Put their party in the majority. If the Dems get the majority in either or both houses then those strong progressive leaders that we do have will have even more power to enact strong progressive action.
Q. What does that mean for Dems who aren't the lucky ones?
A. It means they have to suck it up and vote for the spineless anyway. In fact, it is your duty to do so if you want the strong progressive leaders we do have to have even more power. If you find it hard to pull the lever for a "torture lover" then just think of a Ned Lamont or a Russ Feingold or whoever is your favorite and pull the lever for them.
Your spineless Dem Rep or Senator is your proxy vote for the people you do want to have more power.
They are tools. Use them.