Arguing centrist v. leftist is missing the point, in my opinion.
The political spectrum is not a straight line running from far-left to middle to far-right. The political spectrum is actually a multi-dimensional graph that includes as many points of view as there are people. But for the purposes of this post, I am going to separate our broad liberal coalition into three very general ideological groups.
The names I have chosen for these groups are names I made up myself, and should not be taken to describe anything other than what I say they do. I am using the term "they" to describe each of these groups, although I will admit that I may belong to one or more of them.
Please note that by putting people into broad groups, I run the risk of appearing to stereotype everyone in any particular group. My intent is to provide some framework to describe people, but I am not trying to pigeon-hole any particular person.
But getting back to my original point: Arguing straight centrist v. leftist is missing the point. I believe there are three broad ideological groups in our coalition, and we need to figure out how to appeal to all of them.
Left-liberals - It's pretty obvious that this group is the dominant one on Democratic Underground. It may even be the dominant group among party activists and elites, although I am doubtful that this group is a majority of our voters. This group tends to be liberal across-the-board on all issues, whether they are cultural, social, economic, or foreign policy. They dislike most war, they support abortion, gay rights, gun control, the environment, and they support workers rights, organized labor, progressive and relatively high taxes, and universal health care.
Center-left libertarians - These are the folks who are generally liberal on social issues, support abortion, gay rights, gun control, education, and the environment, but tend to be more fiscally conservative in their economic outlook. They are urban or suburban, they support free trade, they are distrustful labor unions and government regulation. They like balanced budgets. They might have even voted Republican back before the Republican party took a hard-right cultural turn. (To be clear, when I use the term "libertarian" I'm not referring to the generally right-leaning people who might be tempted to support the Libertarian Party.)
Center-left populists - These are the people that support liberal economic policies, but are generally conservative in their social, cultural, or foreign policy views. They may be working class or middle class, working in manufacturing or service industries. They may be in a union, or they know people in a union. They oppose free trade, they support universal health care and workers' rights. But they are conservative culturally, or they are deeply ambivalent about cultural issues. They support things like gun rights, regulation of abortion, a strong military, and protecting the flag, and are skeptical of gay rights and affirmative action. When the country goes to war, it might not even cross their minds to oppose it. To do such a thing strikes them as unpatriotic.
I think most observers would agree that the Democratic party is getting killed among the third group: Center-left populists. The Republican party is making great inroads into this group on an overtly cultural appeal. Party elites in Washington, DC, New York, and California, scratch their heads and wonder why working-class people would possibly vote against their own economic interests.
I think that the simplest answer is this: Their interests are not entirely economic. Like most voters, they vote on a broad range of issues, including cultural issues. But I think there is something else going on here. Maybe the Democratic Party isn't doing such a great job at defending their economic interests.
For as long as I have been a Democrat, we have taken for granted the obvious truth that we are better at protecting the economic interests of the vast majority of Americans. But I think the gradual erosion of support among Center-left populists suggests that they do not have the same opinion of the Democratic Party. Democrats need to figure out how to position ourselves once again as the staunch defender of the economic interests of the middle class.
Here's another problem: I believe that party elites are disproportionately drawn from the first two groups: Left-liberals and center-left libertarians. I know lots of Democrats here in Washington, DC, and they are almost all relatively affluent professional types from the Northeast or West Coast who don't have any life experience at all interacting with regular people from middle America. In fact, their opinion of them could almost be described as contemptuous. At a minimum, I think it could be called condescending. We think that we are doing "those people" a favor by supporting policies which will help them, and quite frankly we feel a little offended that they aren't thanking us for looking out for them.
Quite understandably, the response of some center-left populists is "I'll look out for myself, thanks." Nobody wants to be anyone else's charity-case.
Ultimately, my point is this: There is going to be a lot of fighting about whether we need to go "liberal" or go "centrist," but in the end, I think it's missing the point. As long as urban elites from the Left-liberal group and the Center-left libertarian group are arguing among themselves about "how to win the hearts of populists" we are going to lose. Because, let's face it: Most people don't have that much experience dealing with people who are different from ourselves.
If we want center-left populists to be Democrats, we need center-left populists in our coalition to show us how. We need to value their contributions, and we need to welcome them into our coalition as equal members.
Part of the reason why I am a Democrat (and why anyone is a Democrat) is because I am surrounded by people who share my values and who are all Democrats. Center-left populist Democrats are the members of our party who are most likely to reach other Center-left populists. Let's start valuing their contribution, before we lose them all to the other side.