To bribe or to persuade
The author is speaking about the XIX century...
Even those whose attitude towards public opinion in politics did not change found that of necessity they had to learn the mechanics of peaceful persuasion by propaganda. With an extended franchise and an increasing population it was becoming too expensive to do anything else. Where at one time voters could be bought, they now had to be persuaded. Politicians had, therefore, to become interested in propaganda.
Source: Propaganda and psychology warfare, 1962 by Terence H. Qualter
So, basically, political propaganda (or call it PR) is just a cheaper alternative to bribing the voter.
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