That's the thrust of this article by Stanley Kurtz in National Review:
"Why were we so wrong? Why did Dan Rather and CBS News, against all expectations, impeach their own credibility to defend the authenticity of memos that are almost certainly forgeries? The obvious answer is that they did it to save the faltering Kerry campaign from a final and decisive blow. If CBS were to admit that the documents were forgeries, it would have no grounds for protecting its sources. In fact, CBS would have a positive obligation to do everything in its power to expose the malefactors behind the forgeries. If the trail led back to the Kerry campaign, president Bush's reelection would be assured. Dan Rather has been at pains to derogate those who are interested in where the documents came from. This sounds suspiciously like Rather is concerned about what a revelation of his sources might mean. Certainly, if Rather personally received the forgeries from a Kerry operative, it would be a disaster for Rather. That alone might seem to be sufficient to explain CBS's refusal to admit its error. (It now appears that CBS News may well have received the documents from a partisan and highly questionable source.)
"And even if the trail leading back to the forgers does not pass through the Kerry camp, an admission by CBS that the documents are bogus would be a huge embarrassment for the senator's campaign, which has so aggressively seized upon the story to attack the president. It would also be a fiasco for Dan Rather and CBS, whose credulity on a story harmful to the president would be exposed, and pointedly contrasted to their treatment of the Swift-boat veterans.
"But surely it would have been better for Rather and CBS to cut their losses and admit their error. Yes, they would have taken a hit, but they would also have won kudos for honesty and professionalism. Americans are forgiving of those who admit error. By standing behind a story that is so obviously flawed, Rather and CBS News are setting themselves up to become laughing stocks. That is why the reasonable assumption I -- and many other folks -- made was that CBS would attempt to salvage its reputation by repudiating the memos. And that is why many now assume Dan Rather and CBS News have sacrificed their reputations in order to protect the Kerry campaign."