Michael Signer is mayor of Charlottesville, Va. He is an attorney, a lecturer at the University of Virginia and author of “Becoming Madison: The Extraordinary Origins of the Least Likely Founding Father.”

Donald Trump speaks at the Myrtle Beach Convention Center in Myrtle Beach, South Carolina on November 24. REUTERS/Randall Hill

In the 17th century, poet John Milton called it a “goblin word” — a sobriquet so low that it was reserved for only the most insidious of rabble-rousers — yet in the last few months, any number of observers, from GOP presidential also-ran Rick Perry to former Labor Secretary Robert Reich, from the Economist to, most recently, the New York Times, have crossed a rhetorical line in our politics by calling Donald Trump out as a “demagogue.”

Until recently, I’ve resisted it. As the author of “Demagogue: The Fight to Save Democracy from Its Worst Enemies,” I have been asked countless times in recent years whether Trump is a demagogue, and have always responded — indeed, thought — that he was not. Clearly, though, with his escalating effrontery toward the American creed, he is now.

This is not a matter of mere semantics. In the same way that precision should be used when issuing a terror alert, the term demagogue, properly applied, should be a tocsin of democracy — deployed judiciously and ringing loudly to foretell a singular menace to our republic.

The word dates back to ancient Athens, where the original term in Greek literally meant leader (agogos) of the people (demos). In 1838, American author James Fenimore Cooper observed that true demagogues met four criteria: they posture as men of the common people; they trigger waves of powerful emotion; they manipulate this emotion for political benefit; and they threaten or break established principles of governance.

I used to give Trump a pass on the first and last of those points. It was a bit difficult to regard someone who’s always made such a spectacle of his glitzy skyscrapers and lavish private golf courses as a man of the people. And in the presidential race he seemed, initially, more intent on bringing the parlance of business to governance than on undermining government itself.

But over the last several weeks, Trump has crossed both lines.

Despite his billionaire status, he’s fashioned himself into a mirror of the masses by appealing directly to the anxieties of a  “silent majority” of mostly working- and middle-class white voters.

And he’s come perilously close to sanctioning not only inflammatory language — blithely impugning Latino immigrants and Muslim refugees — but violent behavior, reacting to an incident in which a protester was physically confronted at one of his campaign events by saying, “Maybe he should have been roughed up.” On Sunday’s “Meet The Press,” he called last Friday’s shooting at a Planned Parenthood facility in Colorado Springs “terrible,” but at the same time made a point of remarking on what he described as “a lot of anxiety” and “a lot of dislike for Planned Parenthood” among the supporters who attend his rallies. He’s demonstrated a penchant not only for perpetuating falsehoods, but for doubling down on them, such as the canard that he “watched” as “thousands and thousands” of people in Jersey City cheered the 9/11 attacks — bringing maximal heat and minimal light to the public discourse.

Cooper observed, “The demagogue always puts the people before the constitution and the laws, in face of the obvious truth that the people have placed the constitution and the laws before themselves.” And while, so far, Trump has only said he’d “strongly consider” closing certain mosques and briefly flirted with the idea of instituting a registry for Muslims, even entertaining these proposals undermines our shared civic values.

In different times and places, demagogues have used this approach to build loyal, self-contained constituencies accountable to them alone: in ancient Athens, Cleon, the brutal general who helped depose the statesman Pericles; in the Jim Crow South, segregationist governors Eugene Talmadge of Georgia, Theodore Bilbo of Mississippi and George Wallace of Alabama; more recently, Venezuelan President Hugo Chavez, whose “Capitalism is the way of the devil” refrain now almost sounds like an inverse bookend to Trump’s real-estate-tycoon bombast.

Throughout history, when they appear, demagogues have been seen as existential threats to democracy.

In The Federalist No. 1, Alexander Hamilton warned of leaders who begin “paying an obsequious court to the people; commencing demagogues, and ending tyrants.” At the constitutional convention, James Madison argued that only an extended republic could diffuse “the mischievous influence of demagogues.”

It was with demagogues in mind that the framers devised a series of constitutional checks and balances, including the United States Senate — which Madison described as a “necessary fence” against “fickleness and passion” — and the Electoral College, whose independent electors could, theoretically, stop a demagogue from becoming president.

But even if he doesn’t reach the White House, Trump can still harm the nation in other ways. He already has — by embarrassing the United States on the world stage, dividing Americans against each other and hastening the advent of a “fact-free” presidential campaign.

Just as an autoimmune disease attacks the body through its own defenses, demagogues are a disorder native to democracy itself. It’s no surprise, then, that the word has been invoked most profoundly in democracies concerned about their integrity.

In 1933, Americans watched with alarm as the ultimate demagogue, Adolf Hitler, began subverting Weimar Germany’s fragile democracy from within by turning Germans against their constitution. It was no accident that two years later, Sinclair Lewis published the best-seller “It Can’t Happen Here,” depicting the rise of an American demagogue-cum-tyrant named Buzz Windrip, and Gen. Hugh Johnson pointed to Sen. Huey Long and Father Charles Coughlin as societal menaces “preaching not construction, but destruction.”

The American people understood what they were dealing with then: democracy’s enemy within. And we’d be wise to accurately diagnose it now. Trump is a demagogue. Not just in a casual sense, but in the most powerful meaning of the word, and he should be confronted as such.

If that doesn’t work, there’s always the Electoral College.

Correction: This article originally referenced the subverting of Germany’s Weimar Republic in 1935, but the date has been changed to reflect that several events associated with this history occurred in 1933.