Republican presidential candidate Donald Trump speaks to guests during a rally at Macomb Community College on Mar. 4 in Warren, Mich. (Scott Olson/Getty Images)

Watching John Oliver’s brutal critique of Donald Trump this past weekend, I was struck by the Nevada caucus-goer who said that Trump “tells it like it is.” It’s one of Trump’s strengths. An exit poll taken during the South Carolina Republican primary, for example, reported that 78 percent of voters who said “tells it like it is” was the top quality they’re looking for in a candidate said that they supported Trump.

There’s something particularly powerful about Trump’s rhetorical style. In my book, “The Politics of Sincerity,” I call this style “hyper-sincerity.” When a politician is hyper-sincere, the world can be reduced to simple truths. It’s a view of the world as a clearly knowable, not-all-that-complex place ruled by self-interest and power. And the more hyper-sincere the politician, the less thought needs to go into his language. Why bother with fancy wordplay? Isn’t that what you use when you’re trying to hide something?

This type of hyper-sincere politician has been with us for ages. In my book, I go all the way back to classical Athens, looking at Plato’s response to the straight-talkers of his time. In particular, I focus on Cleon, a demagogue Thucydides wrote about in “History of the Peloponnesian War.”

Both Cleon and Trump disparage the wordiness and thoughtfulness of others. Both claim to be brave enough to stand up to the establishment and lead ordinary people back to greatness. Trump’s calls for expelling Muslims, building walls, expanding the use of torture, and murdering the families of ISIS fighters are still not equivalent to Thucydides’ indictment of Cleon as the “most violent man in Athens,” but there’s been enough violence associated with Trump’s rhetoric and campaign that someone has already made a video compilation.

Thucydides immortalized Cleon as using straight talk as just another rhetorical device used to distract citizens from basic democratic values. For instance, Cleon called on Athenian citizens to authorize the massacre of all the men on the island of Mytilene in retaliation for their rebellion against Athens. That’s more extreme than what we’ve heard from Trump. But both ask their fellow citizens to do things that go against the democratic values of equality and openness and also against their own self-interest – all in the service of righteous anger and in an attempt hold onto their status as the most powerful military force in their world.

Cleon’s outrageousness was seen as a sign of his “parrhesia,” a Greek term for frank speech. Parrhesia was meant to be free from the rhetorical tricks that had grown increasingly common in the ancient city. The concern with frank speech began as an attempt to ensure that the newly democratized Athenians could trust in their democratic debates, especially once the itinerant scholars known as “sophists” began offering the first courses in “rhetoric” – ancient versions of today’s spin doctors.

To speak frankly meant to speak openly and honestly, to give advice to the city without fear or shame. But parrhesia became its own form of spin over time in Athens, a way for demagogues like Cleon to pander to the citizens, reducing a complicated world to black and white, disparaging opponents and increasing their own hold on power. Cleon died in a military campaign a few years after the Mytilinean Debate, but the degeneration of political discourse in Athens continued and the democracy eventually gave way to oligarchy. After the Spartan defeat of the city in 404 BCE, the city was left to slowly rebuild its democratic experiment, with philosophers like Plato sorting through the aftermath.

American politics today has its own version of frank speech — namely, an insistence on sincerity. There’s a belief that politicians should not lie, nor should they distract listeners with verbal fireworks and big words. The idea that a leader might frankly call out the politicians for rigging the game against the less powerful can be deeply appealing in an age of massive and ever-growing income inequality and austerity. Trump is taking full advantage of it. But as happened in Athens, the American concern with sincerity can give some an opening to manipulate this ideal through a demagogic hyper-sincerity.

One common rhetorical trick that frank-talking or hyper-sincere panderers use is to flatter an audience for being smart enough to see through the rhetorical tricks of opponents and instead to bravely face the “truths” you’re offering. Athens’ experience shows us how easily frank speech can become just another form of cynical pandering.

Elizabeth Markovits is associate professor of politics at Mount Holyoke College and author of “The Politics of Sincerity: Frank Speech, Plato, and Democratic Judgment.”