Your excellent questions deserve a separate posting, but let me give a couple of shorter answers. First, the evidence for the increasing polarization of the Senate caused by the shrinking of the moderate middle comes from voting studies that measure the underlying ideology of Senate members. I’ve cited them before, but in short they show that during the last six decades the Democratic party mean ideology has shifted left, and the Republicans right. You can see this without looking at the data – think about a Democratic party of 30-40 years ago, one that contained Fritz Hollings, or Sam Nunn, or Scoop Jackson or any number of conservative Democrats. All gone today.

As Jason points out, and as I’ve remarked many times before in previous posts, politics in the U.S. plays out on a very narrow ideological spectrum – in contrast to many European nations, we lack any socialist party, or royalist party on the right or viable green party or communist party. We are really a center-right nation when compared internationally. That’s why I said from the beginning that we were never going to get a single-payer system, or even anything remotely close. Politics is the art of the possible, and I blog about what’s possible in the United States context, not about what I or others might like to see or about what might happen in other nations, about which I know less than nothing.

What does this mean for health care? Liberals are disappointed that what passed the Senate was, as Jason aptly puts it, a “watered down” bill that lacks, among other elements, a public option. Conservatives, meanwhile, are outraged that it includes a mandate forcing people to buy coverage. I leave it to others to evaluate the merits of these arguments. My point is that the threat of the filibuster, and the need to get 60 votes predictably gave increased leverage to the few Senate moderates left; our voting theories said that people like Nelson would hold the balance of power – and they did. If we step outside the Senate, and think about the public, one can argue that Nelson’s views are closer to the median view of the public (at least as far as the public can be said to have a “view” on health care). This is not to claim that the moderate view is the “right” view. But it may be the dominant view, and if so there’s something to be said about a mechanism that allows that view to be represented in the Senate.

But if I get a chance I’ll address this in a longer post.

The closest thing we have to an extremist on the left in the Senate is our own Sen. Sanders, but he would be a mainstream left-leaning politician in most European countries (and arguably in decades before the 1980s in the US). It seems like you’re defining center as the median between the parties, which is tilts to the right when comparing to other countries or most measures of actual policy goals.

You make a compelling case that Krugman and Klein are posturing for short-term political gain; they certainly don’t seem to be looking to do what they think is right in terms of the political philosophy of republican institutions!

It also seems that Senate Democrats don’t have the political capital to get rid of the filibuster, and also, that it would do a long-term disservice to them as Republicans will certainly control the Senate again, perhaps even in four years.

A possible critique of your thinking, however is that you seem to be valuing compromise or rule from the middle for its own sake. I guess a detached architect of a political regime would want the “moderates” to rule, but in the practice of contemporary American politics, it frustrates me that Ben Nelson is calling so many shots.

Finally you mention: “an increasingly polarized Senate, in which Democrats grow more liberal and Republicans more conservative.” I know this isn’t easy to quantify, but can you substantiate the claim that both sides have moved away from the center? My admittedly biased sense is that, in the past 50 years, Republicans have generally become more conservative, but that Democrats, on the whole, haven’t moved that far to the left.