As a white, male, middle-aged conservative talk radio host from Virginia, John Fredericks is something close to the Platonic ideal of a Fox News fan. And until last year, he was one. But then Fox’s treatment of the Republican primary race — the presentation of Karl Rove as a political analyst despite his having “thrown in for Romney” and Sean Hannity’s clear ties to the Republican establishment — began to grate on him. So he changed the channel.