Today's Trumpology: Is this one of history's rhymes?

For months, I've resisted the temptation to liken Donald Trump to Adolf Hitler. It seems a bit unfair to Hitler.

"To be greatly and effectively wicked, a man needs some virtue," explained C.S. Lewis's devilish connoisseur of human corruptions in "The Screwtape Letters." "What would Attila have been without his courage, or Shylock without self-denial as regards the flesh?"

It's reassuring to suppose that such villains, shorn of their self-mastery, might have resembled the Donald — all bluster and self-regard, but not enough sincere grit to wreak major havoc.

Hitler was a pillar of perverted integrity in Screwtape's sense — driven by maniacal, pitiless commitment to a tribal cause that was entirely evil but not entirely about himself.

Trump's egoism and lack of durable principles may ironically represent Americans' best hope that if worse comes to the worst, a President Trump simply wouldn't have the strength of purpose to be "greatly and effectively" disastrous.

That said, I'm haunted by a memory from a 1993 study trip to Berlin. One day I attended a luncheon hosted by an aging Deutsche Bank executive. Old enough to remember Hitler's rise, he said he'd long struggled to explain to younger people how such a madman hoodwinked a large, sophisticated nation.

He added that as it happened, American politics just then, in the early 1990s, featured a prominent figure with Hitler-style appeal.

The elder German saw neither a racist nor a tyrant in Perot. But the deficit fighter's common-touch populism, his insistence that the people runnin' things was none too bright and us regular folks won't have no trouble fixing up the country once we give the boot to them fancy fakers — that, our host said, was exactly Hitler's act, only in a different dialect.

Another discomforting vision of demagoguery from its heyday was authored by Minnesota's Nobel Prize-winning novelist Sinclair Lewis. In "It Can't Happen Here," in 1935, before the full horrors of Nazism were revealed, Lewis conjured a satire in which U.S. Sen. Berzelius "Buzz" Windrip — "an inspired guesser at what political doctrines the people would like" — imposes fascism on America.

Windrip gets himself elected president with promises one admirer calls "molasses for the cockroaches," including: "that he had thoroughly tested (but unspecified) plans to make all wages very high and the prices of everything … very low; that he was 100 percent for Labor, but 100 percent against all strikes; and that he was in favor of the United States so arming itself, so preparing to produce its own coffee, sugar, perfumes, tweeds and nickel instead of importing them, that it could defy the World … and maybe, if that World was so impertinent as to defy America … take it over and run it properly."

But if Trump's finger-snapping style is nothing new — anymore than the grievances and gullibilities it exploits — the power of popular uprisings can startle keepers of any status quo.

Glenn Reynolds at Instapundit intriguingly detects in Trump's triumphs a "preference cascade," a term coined by Timur Kuran in his book "Private Truths, Public Lies."

As long ago as 1978, in his great Harvard address, Alexandr Solzhenitsyn said: "Without any censorship, in the West … fashionable trends of thought and ideas … frequently prevent independent-minded people from giving their contribution to public life."

But Kuran's and Reynolds' idea is that if once a galvanizing event, a new communications technology or a fearless insurrectionary leader reveals that opponents of an existing order are in fact numerous, even a majority, a rebellious "preference cascade" can overthrow powers-that-be seemingly overnight. Think of the rapid collapse of communism in Eastern Europe and of some Arab Spring revolutions.

Trump does seem to be giving millions of Americans a safe way to express exasperation of various kinds with today's often suffocating cultural/political orthodoxy — secular, internationalist, multicultural and mildly corporatist and collectivist both. And its enemies do seem to have quietly multiplied and diversified. If only hardened racists backed Trump, he'd have faltered before now. Many voters with libertarian or conservative leanings, who have altogether reasonable differences with the prevailing agendas in both political parties, who may be economically pinched and who feel bullied and disrespected on such issues as race and crime, immigration and trade, sexuality and family, religion and national security seem to see in Trump a kind of battering ram and attitudinal liberator, even if many of them hope he doesn't mean everything he says.

Every ruling order faces a dilemma. To welcome too much dissent is to risk contagion. But intimidate heresies too completely and you cease to know how much disagreement exists, or what it consists of, or how to satisfy legitimate protests. Repression welds an alliance between mere critics and implacable enemies and, as in a forest that hasn't suffered a smaller fire in ages, dry tinder accumulates, ensuring a conflagration once a spark is lit. That seems to be something like what's happened, if Reynolds' notion that we're seeing a Trump "cascade" is right.

Trump isn't the GOP nominee yet, much less president. But those who would stop him — or deal with him later, should "it," after all, happen here — need to focus on understanding the cultural divide that has concealed so much smoldering discontent.