Four years later, with Wallace knocked out by a would-be assassin???s bullet, Nixon coasts to a 49-state, 23-point obliteration of mild-mannered prairie progressive George McGovern. ???Nixon was the man meant for the moment,??? says Perlstein, 38, who lives with his wife in Chicago, contributes to numerous publications such as The New York Times and The Nation, and is a fellow at the liberal Campa