But, if there is this liberal/moderate split in the Democratic Party, I haven’t seen any evidence of it.Walter looks at the numbers and draws the wrong conclusion. One only needs to read dailykos and know that there is a divide. Or you could look at the votes of Mark Pryor. Or hear Robert Gibbs scoff at the "professional left." We know there are pro-coal, pro-life, pro-gun, and even pro-business Democrats. To say there's no difference between the positions of Elizabeth Warren and Mark Begich is ludicrous.
What Walter misses is that she's using numbers based on Democrats and Republicans self-identifying which camp they fall into. Republicans have a fairly clean divide between moderate and conservative. For a large part, those that identify as each do differ in where they stand on issues.
If there's no real difference, however, between a moderate and a liberal Democrat, then we're obviously dividing the two groups improperly. Why would you have two terms for people who believe the same thing? Clearly, they're both moderates or both liberals. Walter mentions that "The liberal wing of the Democratic Party is also much smaller than the self-identified conservative wing of the Republican Party." She doesn't ask why. The reason is that some so called "moderate Democrats" are liberals. When you get so many liberals identifying as moderates, then the moderates' positions are going to look a lot like the liberals' positions.
A better way to determine if people are conservative, moderate, or liberal would be to have them do one of those Internet ideology tests we've all taken. Ask them to answer 10 or 20 questions and then classify them thusly. I'm guessing you'd see a broad range of answers from people who identify as Democrats. Once you've identified people who are actually liberal and actually moderate, I'm guessing you'll see some kind of divide in the "deficit/spend on the poor" question she uses.