Nate Silver explains why:

I think some of you are underestimating the percentage of voters for whom Sarah Palin lacks the standing to make this critique of Barack Obama.

To many voters, she is either entirely unknown, or is known as an US Weekly caricature of a woman who eats mooseburgers and has a pregnant daughter. To change someone's opinion, you have to do one of two things. Either, you have to be a trusted voice of authority, or you have to persuade them. Palin is not a trusted voice of authority -- she's much too new. But neither was this a persuasive speech. It was staccato, insistent, a little corny. It preached to the proverbial choir. It was also, as one of my commentors astutely noted, a speech written by a man and for a man, but delivered by a woman, which produces a certain amount of cognitive dissonance.

This was the moment that McCain surrendered to the base who once despised him.

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