Sarah Palin did us all a favor during the 2008 Presidential campaign by revealing her stunning ignorance of nearly everything essential for a Vice-Presidential candidate to know. Her name is now and forever synonymous with the term “rural rightwing cluelessness,” and thank God for that clarity. Not that this matters to the righties in the bubble. They can shut out anything. They’re Jedi Masters at that.

If you’ve read John Heilemann and Mark Halperin ‘s “Game Change,” a well-vetted history of the ’08 campaign on both sides, the content of Jay Roach‘s Game Change, which focuses only on the McCain-Palin side of things, will add nothing to your knowledge of Palin’s antics. The film does, however, make clear how thick she really was, and it does, in my view, seal her political tomb with fresh warm cement.

Game Change (HBO, debuting Saturday) is absolutely vital viewing, and not just because it’s great truth candy. It also delivers two superb performances — Woody Harrelson‘s as McCain campaign manager Steve Schmidt and Julianne Moore as Palin. Both will be up for Emmy’s later this year, trust me.

There are two phases in both performances. For the first 30 or 35 minutes Schmidt and Palin are about ambition, anticipation and excitement. And when it starts to becomes clear what a myopic boob Palin is and how little she knows (and what great fodder this is becoming for the liberal media), they’re both enveloped by increasing levels of shock.

Harrelson is especially effective at conveying a sense of steadily building alarm that gradually morphs into something close to terror. Moore is playing the source of that, of course, so I didn’t feel the same empathy, but she’s awfully good at portraying a woman under the influence of all sorts of horrible denials and suppressions.

On top of which Game Change is a fascinating political drama that just tells what happened (everything has been vetted and verified), and yet is not really about “what happened” as much as a portrait of how the political arena changed four years ago — how an insubstantial woman and a very substantial man both ascended to great political heights on the strength of their personal metaphors and natural charismatic appeal. Barack Obama had the smarts and the patter and political background and Palin didn’t…but they were both manifestations of the same cloth.

I was also moved and persuaded by Ed Harris‘s portrayal of John McCain and especiallly Sarah Paulson‘s as Nicolle Wallace, a senior McCain campaign adviser who was charged with trying to prepare Palin for her various press encounters. In fact, this is the first performance Paulson has given that has prompted me to stand back and go “whoa.”

Because it’s an accurate retelling Game Change is not on Palin’s side. It couldn’t be. It’s mainly Schmidt’s story with a seasoning of Wallace for added pathos. They both suffered greatly, but it was Schmidt who urged McCain to pick Palin as his running mate so he’s got the python wrapped around his neck. I’ve been there. I’ve made mistakes that won’t go away, and I know what kind of hell that can be. This is one of Harrelson’s best-ever performances. I liked it better than his work in Rampart, and that’s saying something.