I disagree. Rush is in a shrinking medium. AM radio was already losing listeners to FM when he came about. It was simple demographics. Music sounded better on FM and thus the younger crowd abandoned AM. The talkers at the time were moved from the night slots to the days. Rush got to fill those day voids following in the coat tails of Barry Farber, Barry Grey, Bob Grant, etc.
Political radio programming is a niche, not a medium. Big fish in a small pond. They syndicate into markets that don't even have zip codes. That was the problem with AirAmericaRadio. They couldn't sell as much soap as the established station's shows. They thought they were going to grab the younger crowd but they weren't there. It was like trying to sell Xbox in a senior citizen home. Do not think in any way that that political broadcasting ratings transfer into a nation's political thought. Most people eligible to vote never vote.