Both Plato and Cicero argued that the best orator is a philosopher, or, at least, a good person or person of virtue. If you were not a philosopher or a good person, you were not an orator but merely a sophist or demagogue.
Against this, we have to contend with the fact that even a wretch like Hitler was able to move crowds—and quite powerfully and world-historically at that. Everything about Hitler was warped, his character (ethos), the arguments he used (logos), and the emotions that he sought to instil (pathos), but, still, people followed him in their droves because they themselves were wretched and warped.
A lesson from Aristotle
Plato’s long-time student Aristotle, who lived some twenty-four centuries ago, was perhaps the first to understand that the bedrock of democracy is an affluent, educated middle class.
In the Politics, Aristotle says that, compared to states with a large middle class, states of the rich and poor tend to strict oligarchy (“rule by a few”) or rampant democracy, and, ultimately, to tyranny.
Unfortunately, few states have a large middle class, so that the middle, balanced form of government is rare. According to Aristotle, a democracy becomes preferable when the quantity of the poor exceeds the quality of the rich. Otherwise, an oligarchy is preferable.
The form of the democracy or oligarchy depends on the precise composition of the state. But in every case, the middle classes ought to be included in government, because only they are able to successfully mediate and arbitrate between the rich and the poor.
What we can do right now to protect against demagogues
If today’s democratically elected governments wish to preserve and perpetuate the system that elected them, and that ensured an unprecedented eighty years of peace, they need to introduce better, stronger safeguards and balance an excess of democracy with oligarchy, or, to be more precise, aristocracy (“government by the best”) or repositories thereof—such as tighter rules and more stringent criteria for selecting political party leaders and a more independent or autonomous judiciary.
But for the longer term, they need to look to the economy, social justice, culture, and education. Because rhetoric, or oratory, is not carried out in a vacuum. What is ethos, what is pathos, even what is logos alter according to the dispositions and inclinations of the audience or public—although I do believe that, overall, and over time, with the lessons having been learnt, the good, the true, and the just are naturally more persuasive.
No tyrant lives forever. Now war rages on forever. Men come and go as leaves year by year upon the trees, and every second or third generation must learn the lessons anew.
Or read.