How did a likable, consensus-oriented governor become such a divisive figure? This is a different and deeper scandal, in which many are implicated.

At the beginning, Palin was given plenty of reasons for grievance. After her selection as John McCain’s running mate, some in the press focused unkind attention on her family and faith. From a human perspective, her defensive reaction was understandable. In a memorable convention speech, Palin returned a volley of fist-shaking populism. On the campaign trail, huge Republican crowds — far larger than McCain generally drew — rewarded Palin’s feistiness. It was the heartland (including the tundra) against the coasts; real Americans against the elites. Following the election, a procession of radio and cable appearances further simplified and purified Palin’s persona. Positive reinforcement had done its predictable work. The candidate became a caricature. The caricature became a celebrity.

This transformation would be easier for the media to criticize if they did not frequently fall for the same temptation. Audiences for blogs, radio talk shows and cable television tend to reward ringing reassertions of their own certainties. It is not just politicians who build followings with predictable, partisan arguments, vividly expressed. Simplicity is salable. Doubt and complexity are not. Extreme statements attract attention. Soon they predominate. Eventually they define. A pose becomes a brand. A mask becomes a face.