What industry did politicians use to spread information about their own party and opponents?

Here's a fact about Politics: It walks holding hands with Propaganda.

This tool that persuades and convinces the voters about some certain information, usually explicit during the sending of messages;

Propaganda serves also as a tool of governance, but in the political environment, it is a weapon against political opponents and the opposition in general. The best example of government propaganda is the Public Service Announcements.