The quality to which every anti-rhetorician aspires is authenticity. But there is a big difference between proclaiming your authenticity and actually being true to yourself and the facts. So let me use a different term: authenticism, for the philosophical and rhetorical strategy of emphasizing the “authentic” above all.

Modern authenticism began as a reaction to the Enlightenment program to recast language to conform to the notion of Reason. Immanuel Kant’s friend Johann Georg Hamann was one of the first to make the case that, if you take ideas and words out of their behavioral and cultural context, they lose meaning and relevance. A purely rationalist language would no longer be able to express community or faith. Hamann’s contemporary, the philosopher Johann Gottfried Herder, made the critical link between language, culture and nationhood, and soon authenticity of language became associated with another product of Enlightenment thought: nationalism.

These ideas entered European thought through a chain of influence that stretched from Hegel to Kierkegaard to Nietzsche. By the early 20th century, Martin Heidegger was distinguishing not just between authentic and inauthentic modes of being, but between authentic and inauthentic language.

“Once you heard the voice of a man, and that voice knocked at your hearts, it wakened you, and you followed that voice.” That was Adolf Hitler, the man whom Heidegger would praise for helping the German people rediscover their authentic essence, addressing government and Nazi party leaders in September 1936. According to Hitler, the miraculous appearance of the “voice” — by which he meant the profound bond between himself and his audience that let him express their deepest feelings — allowed ordinary men and women, who were “wavering, discouraged, fearful,” to unite as a Volk, or national community. It was at once a political and a personal “voice” that, thanks to the invention of radio, could reach out not just to audiences at political rallies, but into any living room.

Authenticism was banished to the fringes of politics after World War II and the defeat of European fascism. Technocratic policy-making delivered relative prosperity and security for the majority, and many voters found the rationalist rhetoric of mainstream politicians credible. Authenticism does not even rate a mention in George Orwell’s landmark 1946 essay “Politics and the English Language.” But the uncertainty and division that have followed the global crash, mass migration and the West’s unhappy wars in the Middle East have given it a new opportunity.

Today’s authenticists come in many different guises, from pure anti-politicians like Mr. Trump and Italy’s Beppe Grillo to mainstream mavericks as diverse as Britain’s Boris Johnson and Ted Cruz. None of them are Hitlerian in intent, but nationalism typically looms large (“Make America Great Again!”), as does the explicit or implicit contrast between the chosen community and a dangerous or unacceptable “other,” which in 2016 almost always means elites and foreign immigrants.

They also like to contrast their own down-to-earth way of speaking with the complex and, to many ordinary voters, bewildering language of technocracy. As Michael Gove, one of the leading campaigners for Brexit in the recent British referendum, succinctly put it: “People in this country have had enough of experts.”