This site has a really good diagram of the difference between immediacy and hypermediacy. One difference is that immediacy is like a virtual reality while hypermediacy is like tv news reports
The New Yorker's Ezra Klein breaks down why a skillful use of rhetoric will not always help a President achieve his purpose. This goes back to the point that one's audience will have people who have differing purposes and, in many cases, it will be impossible to persuade everyone.