“Half Nelson” is that rarest of marvels — an American fiction film that wears its political heart on its sleeve. It’s a small film with a long view, and its story hinges on an unusually nuanced relationship between a white man and a black girl, each of whom has landed in harm’s way. The delicacy of its lead performances (more on them later) and its sense of everyday texture are each worthy of praise. But what makes “Half Nelson” both an unusual and an exceptional American film, particularly at a time when even films about Sept. 11 are professed to have no politics, is its insistence on political consciousness as a moral imperative.
