One of the interesting dynamics of political discourse is the use of campaign surrogates — third parties who act as spokesmen or “attack dogs” for the candidate. It is always helpful to have a surrogate with a non-partisan image, which was why Zell Miller was such an effective surrogate for Bush’s 2004 campaign, and why John McCain is grateful to have Joe Lieberman on his side this year.

This is why Republicans have complained so bitterly about the media’s liberal bias over the years. The careful student of this phenomenon will note the tendency of network news reporters to present accusations against Republicans as if the accusations were self-evidently legitimate, often without adequately identifying the partisan origin of the charges. The passive voice — “President Bush came under fire today …” — is used to distract viewers from the source of the criticism. Democratic talking points are repeated without being identified as such.

How does this happen? Mark Finklestein and Matthew Sheffield at Newsbusters catch MSNBC’s Andrea Mitchell arguing that Obama didn’t play the race card yesterday because reporters covering the campaign didn’t think he did so. Where reporters sympathize with the candidate and share his political worldview, the candidate’s rhetoric tends to be viewed as inherently legitimate. And because the press corps is overwhelmingly liberal, the sort of water-cooler conventional wisdom that shapes the media consensus tends to hinder recognition of unfair tactics by Democrats. Thus do liberal reporters function as Democratic campaign surrogates.