For centuries, people had read politicians' words. On Nov. 2, 1920, the first broadcast from a licensed radio station was broadcasting the results of that year's presidential election.

Radio made it possible to listen to politicians in real-time. It meant that personalities started to matter more; the way their voices sounded made a difference. Their ability to engage and entertain became crucial components.

In 1964, media theorist Marshall McLuhan said that "the medium is the message," meaning that the kind of medium through which a message is transmitted matters more than its content.

For centuries, the primary medium for mass political news was the printed word. Political c...