Kevin Drum posted a solid piece about the Obama administration's disconnect with the progressive left.
But only 20% of the electorate self-IDs as liberal. So the math is exactly the opposite: you need to win nearly all the moderates in order to win an election. If you piss off centrists by playing too hard to the base, you'll lose.
This is a bummer, but it's reality, and lefties really need to suck it up and get less annoyed by the fact that politicians react to the world as it is, not as we wish it were. Like it or not, most pols just can't afford to give the liberal base too much rhetorical lip service until and unless it gets a lot bigger than it is today.
One of the reasons I'm going here again, is to emphasize a point about the self-ID numbers, and specifically how they're often misinterpreted -- taken way too literally. Two brief but important points:
1) The word "liberal" is so haggard and stigmatized, pollsters might as well ask people whether or not they consider themselves "effete elitists," because that's the connotation. So, naturally, very few people are inclined to label themselves as such.
2) If you go through the issue-by-issue polls, Americans are more liberal than they own up to. Pro-choice, pro-same-sex marriage, pro-gun laws, pro-Social Security, pro-Medicare, pro-environment, etc.
The political discourse and decision-making in Washington would greatly benefit from exploding that super stupid self-ID poll.