This is a question to which I've never received a great answer. Why does the right have such a complete lock on our national discourse? If the left is the party of writers, artists, intellectuals, shouldn't we be the best word-slingers? The New York Times Magazine attempted to address the first part of that question again this weekend, with an article by Farhad Manjoo. (Digby's comments on the article are here.) Basically the right repeats every slur relentlessly, until it becomes something everyone thinks they know. People don't even know where the slander comes from, or whether or how often it's been debunked. Because they've heard it so many times--even from the same person--it seems familiar, and familiar (according to psychological testing) = true.
I asked Hayden White a similar question a few years ago, and he said the problem is that the right has mastered "normative" language--in other words, they speak to our deep, collective desire to be "normal." The left may not even know this language, because (as artists, intellectuals, etc.) we are outsiders. We spend our lives extolling and defending the different. I suppose by making something sound familiar by repetition, one also makes it normal--something everybody who is normal knows. And how do we cut through this falsely comforting haze of familiarity? The familiar, after all, is the primal urge of conservatism.
I think one step would be to associate that need for familiarity with fear. The right manipulate fear, but we should constantly call them on it. Not just by saying they're fear-mongers, but that they are afraid themselves. They are scared little boys and girls quivering in their caves, while the rest of us want to go out and become better. The American self-improvement imperative could help here.