You got it all backwards, comrade. Cindy Sheehan has not "managed" to become a household word - she was made into one by that part of the elite and their media that decided to oppose the war. Most (many?) Americans have not "shifted their opinion on the war" - but instead they were told by the media controlled by the part of the elite that has decided that the war dos not further its interests anymore that it is time to switch attitudes toward the war.
In short, this is how social movements work. There are always plenty of dissenter groups on the periphery of every society. They are just that - obscure and marginal dissenting groups kept at three arm length from any hall of power and the mainstream political discourse. However, when the political balance of power shifts, parts of the ruling elite may find it advantageous to bring in some external support to its cause. This is when these obscure marginal dissident groups get their 15 minutes of fame - when the elite's attention, and the media's camera with them turn on them and present them as "vox populi."
This is the only chance that these obscure and marginal groups ever have. If they are smart, they manage to get coopted to the elite's orbit. If they are not so politically savvy and insist on their ideological purity, they fall back into oblivion as soon as their usefulness as the poster boy of "vox populi" expires. According to William Gamson (_The Strategy of Social Protest_) this is what happened to virtually every social movement in this country.
In short, being coopeted to the elite's orbit is the best thing that any social movement in this country can hope for. Cindy Sheehan has been coopted - for now. Let's see how she and her supporters will stay coopted.
Wojtek