The key to the ultimate effectiveness of a documentary like “The Undefeated” is more than just how many people see it or even who those people are. Certainly that matters to some degree, but so does how the very existence of the documentary changes the national political conversation. Naysayers of the “The Undefeated” dismiss the film’s impact by telling us that only Palinistas are going to bother to buy tickets. In other words, since the film preaches to the choir there will be no new converts. Intentionally or not, that’s a fairly simplistic declaration that doesn’t take into account how...