Limbaugh came up with a simple, minimum effort program format for a very targeted audience: spirited, bigoted commentary on the recycled political commentary of other pundits. No guests, no research, no background knowledge of any of his topics. A quick sampling of his callers indicates that his audience of approximately 13 million constitutes the country's lowest common denominator from an intellectual standpoint (save, perhaps, those who can't figure out how to work a radio). They seem to require nothing more of him than a Right On! style approval of their incuriousity, ignorance, and social dysfunction. He frequently refers to these listeners as family, and, being a one year college flunk out himself, they really are his peeps in many ways.
Except, of course, for his 33 million dollar a year income. Rush's target listener is white, uneducated, lower middle class, and dissatisfied.
Limbaugh's is a repetitive formula, the Big Mac of radio, and it captures a similar quantity over quality consumer.
As for any actual political sway, it's hard to imagine he has much. His audience just isn't that large. Neither liberals nor folks in the political center, which share a healthy dose of solid, liberal, middle class values of kindness and an aversion to cruelty and bullying, don't listen to his show: it's too boring and offensive. 15 minutes of Rush and you've heard the only song he'll ever sing. His regular listeners are on the KKK end of the political spectrum; they wouldn't get within a light year of the political center; there's nothing to sway there.