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 candidates were expected to participate in a series of debates that were attended by thousands, but millions followed the debates through newspaper accounts. By the 1930s, politicians could address citizens directly through radio. McLuhan described the radio as a "hot" medium because speeches could incite passions.