Four years ago, I wrote an article for TNR's 90th anniversary issue making the case that domestic liberalism is fundamentally about empiricism. Another way of putting it is that there's really one one true ideological tendency in American politics, and that's conservatism. Conservatism has a strong a priori belief about the proper size of government--a belief that big government is wrong even if it accomplishes its stated goals. Liberalism has no a priori belief about the size of government. While liberals do not always agree with each other about what programs or roles are proper, they share a defining quality that empirical results are the measure of a program. A conservative would say that getting government out of the business of health care is a success in and of itself. A liberal would not say that putting government into the health care business is a success in and of itself--it would only be a success if it was found to provide health care at a certain cost, and so on.
A central part of Barack Obama's political identity rests on this premise. There is constant confusion about what he means he he invokes pragmatism and disdains ideology--is he saying he's not really liberal? The answer is, he's not saying that. He's describing liberalism, properly, as a form of empiricism. Take this passage from his inaugural speech:
What the cynics fail to understand is that the ground has shifted beneath them--that the stale political arguments that have consumed us for so long no longer apply. The question we ask today is not whether our government is too big or too small, but whether it works--whether it helps families find jobs at a decent wage, care they can afford, a retirement that is dignified. Where the answer is yes, we intend to move forward. Where the answer is no, programs will end. And those of us who manage the public's dollars will be held to account--to spend wisely, reform bad habits, and do our business in the light of day--because only then can we restore the vital trust between a people and their government.
The reference to "stale political arguments" sounds like a slap at both the right and the left. But in fact it's only a slap at the right. Conservatives are the only ones who think the size of government is an end rather than a means. Liberals are the ones who only care about what works. This isn't to say that liberals are always right about what works, or that they always agree with each other about what works, only that this question matters to liberals in a way it doesn't matter to conservatives. Nor is this to say that moral agnosticism about the size of government isn't also an ideological choice.
Anyway, one of the things I've always liked about Obama is that he thinks and speaks very explicitly along the lines I described in that piece. If you want to understand how he can be without tension a solid liberal and a very strong pragmatist, give it a read.