Ancient philosophers and statesmen saw such demagogues as keys to a devastating “cycle of regimes.” The Greek historian Polybius observed that a demagogue who was “sufficiently ambitious and daring” could capture the people’s favor, where they “once more found a master and a despot.” What followed the demagogue’s “reign of mere violence”? “Tumultuous assemblies, massacres, banishments.”

Ancient Athens had tried to break this cycle. After suffering through ruinous wars and rampant corruption brought on by a spate of demagogues, Athens passed a law allowing citizens to vote, using small pieces of pottery on which they scratched names, to ostracize—to exile for 10 years—any politician “violating democratic principles.” As The Economist recently noted, Athenian ostracism was equivalent to impeachment and was “at the heart of the Athenian political system.”