Maybe spineless Democrats are just responding to their supporters after all.
There's a partisan divide over the issue of political compromise versus ideological steadfastness, according to a newly released USA Today/Gallup poll.
When asked about the "best approach for political leaders to follow in Washington," 41% of Republican respondents maintain that "it is more important for political leaders to stick to their beliefs even if little gets done," while only 18% of Democratic respondents express the same sentiment. This contention is put in opposition to the claim that "it is more important for political leaders to compromise in order to get things done," which 59% of Democrats support versus only 32% of Republicans.
You see this dynamic among Democrats who bend over backwards to give Republicans the benefit of the doubt, or who rush to their defense when they think a Republican has been unfairly attacked, or when they justify the latest Democratic capitulation to GOP (and corporatist Dem) obstruction.
So it seems to work like this: Democrats want Democrats who stand for something! But it's okay to compromise those ideals! But wait, you surrendered those ideals? Okay, I'm sitting this one out!
My half-baked theory is that partisans are responding to the rhetoric of their leaders. Republicans speak forcefully about defending their principles as they stand firm in the way of Democratic communism. Democrats speak forcefully about nothing, apologize constantly for being Democrats, and literally beg Republicans for bipartisan cover for their initiatives.
If the Democratic leadership acted with confidence, their supporters might actually follow suit.
Update: Another theory -- Democrats like compromise, but only in the abstract. From a 2007 Pew poll:
The public's taste for compromise and moderation is limited by several factors. First, while political leaders who are willing to compromise are viewed as appealing, so too are those who demonstrate political conviction. Two-thirds say they like politicians who stick to their positions, even if unpopular. There also is much greater support for compromise in principle than there is on contentious issues, such as the war in Iraq and abortion policy. On abortion, 72% of those who favor either party's stance on the issue say that party should stick to its position, even if that means less progress is achieved.