Why Do Radical Voters Go Out With Centrist Candidates?, or, More on Progressives' Obama Buyer's Remorse

Following on to Michael Moynihan and Damon Root's blogging yesterday on some left-wing Obama regrets, Daniel Larison at American Conservative, spinning off of Glenn Greenwald's commentary on progressive laments about the mainstream nature of Obama's appointments, offers some reasons why non-centrist voters will inevitably live to be disappointed by supporting centrist candidates:

At every stage, the "impractical" purist hears that he should not withhold his support from the marginally preferable candidate under any circumstances. He is urged to be realistic, and so he and those like him do not insist that the candidate make strong commitments on policy positions that are deemed by someone to be out of the mainstream. The candidate pays some minimal lip service to the purist's "values," and this is supposed to count for something. In the name of pragmatism, the purist decides that he has to support the candidate, because the candidate represents the best chance of advancing his views, but even before the election is held the purist has already given so much away in the name of pragmatism and realism that he and those like him have no leverage at all. Having yielded and given away their support in exchange for nothing more than lip service, the purists are scarcely in a much better position than before. They can take satisfaction in being on the winning side, but for the most part this means that they will bear the burden if the public turns against the candidate after he is elected and otherwise they will scarcely get much of anything. The purists-turned-pragmatists will receive the blame for enabling the administration in whatever it does, but they will receive no credit or acknowledgement that their support was important enough to merit meaningful concessions to their concens. Having refused in the first place to exact a price for their support, they have made their support worthless and ensured that they will have no influence.

This applies to libertarian support of most Republican candidates as well.