A supporter holds a sign during a campaign stop by Republican presidential candidate Donald Trump in Nashua, N.H. (John Minchillo/Associated Press)

MANY “ISMS” have been invoked to describe Donald Trump’s presidential campaign, or to define its ideology: nativism, protectionism, racism and, of course, fascism. There’s an element of truth, as well as hyperbole, in each of these descriptors; but none quite captures the essence of Mr. Trump’s improbable, troubling, run. For that, you have to bring in another “ism”: cynicism.

Obviously, politics is not for the ingenuous, and never has been. Politicians have been spinning and manipulating voters since George Washington’s time. Few, though, have done so quite as brazenly as Mr. Trump has. Early on, he touted his unprincipled past as a demanding financial supporter of both parties — “I give to everybody; they do whatever I want” — as if acknowledging participation in corruption qualified him to fix it. He disdained any serious attempt to lay out his policy plans, offering preposterously simplistic solutions instead (e.g., a wall on the southern border to keep out Mexicans, paid for by Mexico). And when confronted with reasonable challenges from the media or other candidates, he responded with schoolboy insults or outright lies (e.g., denying that he had advocated a 45 percent tariff on Chinese goods, despite a New York Times audiotape proving otherwise).

In short, the Trump campaign seems built on proving H.L. Mencken’s observation that “no one ever went broke underestimating the intelligence of the American people.” Or, as Mr. Trump rather chillingly put it: “I could stand in the middle of 5th Avenue and shoot somebody and I wouldn’t lose voters.”

We would hardly absolve his Republican rivals in this regard; they have responded to the Trump phenomenon with varying degrees of denial, avoidance and, alas, imitation. Still, Thursday night’s GOP debate, which Mr. Trump boycotted in a fit of pique at Fox News moderator Megyn Kelly, offered a ray or two of hope that GOP candidates are capable of appealing to the public’s better angels. With Mr. Trump occupied at a bizarre purported fundraiser for veterans elsewhere in Des Moines, former Florida governor Jeb Bush blasted the front-runner’s proposed temporary ban on Muslim immigration, saying it “creates an environment that’s toxic in our own country.” Sen. Rand Paul of Kentucky spoke in affecting detail of the plight of African Americans in Ferguson, Mo., calling on his party to tackle their concerns and thereby broaden its appeal.

The less Mr. Trump dominates the debate, the more room there might be for this kind of discourse.

It may indeed be the case that most Republicans or, someday, most Americans will take Mr. Trump’s offer to be a bully on their behalf. But Mr. Trump’s supposed mind-meld with the electorate, though documented in polls, has yet to be tested in actual voting. Citizens have not confirmed, in a binding way, their desire to be led by a man who so manifestly does not respect them. There is still time to prove otherwise; the GOP caucuses open in Iowa on Monday at 7 p.m.