In The History of the Decline and Fall of The Roman Empire, Edward Gibbon luridly evokes the Rome of 408 A.D., when the armies of the Goths prepared to descend upon the city.

The marks of imperial decadence appeared not only in grotesque displays of public opulence and waste, but also in the collapse of faith in reason and science.

The people of Rome, Gibbon writes, fell prey to “a puerile superstition” promoted by astrologers and to soothsayers who claimed “to read in the entrails of victims the signs of future greatness and prosperity.”

Would a latter-day Gibbon describe today’s America as “decadent”? I recently heard a prominent, and pro-American, French thinker (who was speaking off the record) say just that.

He was moved to use the word after watching endless news accounts of U.S. President Donald Trump’s tweets alternate with endless revelations of sexual harassment.

I flinched, perhaps because a Frenchman accusing Americans of decadence seems contrary to the order of nature. And the reaction to Harvey Weinstein et al. is scarcely a sign of hysterical puritanism, as I suppose he was implying.

And yet, the shoe fit. The sensation of creeping rot evoked by that word seems terribly apt.

Perhaps in a democracy the distinctive feature of decadence is not debauchery but terminal self-absorption— the loss of the capacity for collective action, the belief in common purpose, even the acceptance of a common form of reasoning.

We listen to necromancers who prophesy great things while they lead us into disaster. We sneer at the idea of a “public” and hold our fellow citizens in contempt. We think anyone who doesn’t pursue self-interest is a fool.

We cannot blame everything on Donald Trump, much though we might want to. In the decadent stage of the Roman Empire, or of Louis XVI’s France, or the dying days of the Habsburg Empire so brilliantly captured in Robert Musil’s The Man Without Qualities, decadence seeped downward from the rulers to the ruled.

But in a democracy, the process operates reciprocally.

A decadent elite licenses degraded behavior, and a debased public chooses its worst leaders. Then our Nero panders to our worst attributes — and we reward him for doing so.

“Decadence,” in short, describes a cultural, moral, and spiritual disorder — the Donald Trump in us. It is the right, of course, that first introduced the language of civilizational decay to American political discourse. A quarter of a century ago, Patrick Buchanan bellowed at the Republican National Convention that the two parties were fighting “a religious war … for the soul of America.”

Former Speaker Newt Gingrich (R-Ga.) accused the Democrats of practicing “multicultural nihilistic hedonism,” of despising the values of ordinary Americans, of corruption, and of illegitimacy. That all-accusing voice became the voice of the Republican Party. Today it is not the nihilistic hedonism of imperial Rome that threatens American civilization but the furies unleashed by Gingrich and his kin.

The 2016 Republican primary was a bidding war in which the relatively calm voices — Jeb Bush and Marco Rubio — dropped out in the early rounds, while the consummately nasty Ted Cruz duked it out with the consummately cynical Donald Trump.

A year’s worth of Trump’s cynicism, selfishness, and rage has only stoked the appetite of his supporters. The nation dodged a bullet last week when a colossal effort pushed Democratic nominee Doug Jones over the top in Alabama’s Senate special election.

Nevertheless, the church-going folk of Alabama were perfectly prepared to choose a racist and a pedophile over a Democrat. Republican nominee Roy Moore almost became a senator by orchestrating a hatred of the other that was practically dehumanizing.

Of course, he has legitimized the language of xenophobia and racial hatred, but he has also legitimized the language of selfishness. During the campaign, Trump barely even made the effort that Mitt Romney did in 2012 to explain his money-making career in terms of public good. He boasted about the gimmicks he had deployed to avoid paying taxes.

Yes, he had piled up debt and walked away from the wreckage he had made in Atlantic City. But it was a great deal for him! At the Democratic convention, then-Vice President Joe Biden recalled that the most terrifying words he heard growing up were, “You’re fired.”

Biden may have thought he had struck a crushing blow. Then Americans elected the man who had uttered those words with demonic glee. Voters saw cruelty and naked self-aggrandizement as signs of steely determination.

Perhaps we can measure democratic decadence by the diminishing relevance of the word “we.” It is, after all, a premise of democratic politics that, while majorities choose, they do so in the name of collective good.

Half a century ago, at the height of the civil rights era and Lyndon B. Johnson’s Great Society, democratic majorities even agreed to spend large sums not on themselves but on excluded minorities. The commitment sounds almost chivalric today. Do any of our leaders have the temerity even to suggest that a tax policy that might hurt one class — at least, one politically potent class — nevertheless benefits the nation?

There is, in fact, no purer example of the politics of decadence than the tax legislation that the president will soon sign. Of course the law favors the rich; Republican supply-side doctrine argues that tax cuts to the investor class promote economic growth.

What distinguishes the current round of cuts from those of either Ronald Reagan or George W. Bush is, first, the way in which they blatantly benefit the president himself through the abolition of the alternative minimum tax and the special treatment of real estate income under new “pass-through” rules.

We Americans are so numb by now that we hardly even take note of the mockery this implies of the public servant’s dedication to public good.

Second, and no less extraordinary, is the way the tax cuts have been targeted to help Republican voters and hurt Democrats, above all through the abolition or sharp reduction of the deductibility of state and local taxes. I certainly didn’t vote for Ronald Reagan, but I cannot imagine him using tax policy to reward supporters and punish opponents.

He would have thought that grossly unpatriotic. The new tax cuts constitute the economic equivalent of gerrymandering. All parties play that game, it’s true; yet today’s Republicans have carried electoral gerrymandering to such an extreme as to jeopardize the constitutionally protected principle of “one man, one vote.”

Inside much of the party, no stigma attaches to the conscious disenfranchisement of Democratic voters. Democrats are not “us.”

Finally, the tax cut is an exercise in willful blindness. The same no doubt could be said for the 1981 Reagan tax cuts, which predictably led to unprecedented deficits when Republicans as well as Democrats balked at making offsetting budget cuts.

Yet at the time a whole band of officials in the White House and the Congress clamored, in some cases desperately, for such reductions. They accepted a realm of objective reality that existed separately from their own wishes. But in 2017, when the Congressional Budget Office and other neutral arbiters concluded that the tax cuts would not begin to pay for themselves, the White House and congressional leaders simply dismissed the forecasts as too gloomy.

Here is something genuinely new about our era: We lack not only a sense of shared citizenry or collective good, but even a shared body of fact or a collective mode of reasoning toward the truth.

A thing that we wish to be true is true; if we wish it not to be true, it isn’t. Global warming is a hoax. Barack Obama was born in Africa. Neutral predictions of the effects of tax cuts on the budget must be wrong, because the effects they foresee are bad ones.

It is, of course, our president who finds in smoking entrails the proof of future greatness and prosperity. The reduction of all disagreeable facts and narratives to “fake news” will stand as one of Donald Trump’s most lasting contributions to American culture, far outliving his own tenure.

He has, in effect, pressed gerrymandering into the cognitive realm. Your story fights my story; if I can enlist more people on the side of my story, I own the truth. And yet Trump is as much symptom as cause of our national disorder.

The Washington Post recently reported that officials at the Center for Disease Control were ordered not to use words like “science-based,” apparently now regarded as disablingly left-leaning. But further reporting in the New York Times appears to show that the order came not from White House flunkies but from officials worried that Congress would reject funding proposals marred by the offensive terms.

One of our two national political parties — and its supporters — now regards “science” as a fighting word. Where is our Robert Musil, our pitiless satirist and moralist, when we need him (or her)?

A democratic society becomes decadent when its politics, which is to say its fundamental means of adjudication, becomes morally and intellectually corrupt. But the loss of all regard for common ground is hardly limited to the political right, or for that matter to politics.

We need only think of the ever-unfolding narrative of Harvey Weinstein, which has introduced us not only to one monstrous individual but also to a whole world of well-educated, well-paid, highly regarded professionals who made a very comfortable living protecting that monster. “When you quickly settle, there is no need to get into all the facts,” as one of his lawyers delicately advised.

This is, of course, what lawyers do, just as accountants are paid to help companies move their profits into tax-free havens. What is new and distinctive, however, is the lack of apology or embarrassment, the sheer blitheness of the contempt for the public good.

When Teddy Roosevelt called the monopolists of his day “malefactors of great wealth,” the epithet stung — and stuck. Now the bankers and brokers and private equity barons who helped drive the nation’s economy into a ditch in 2008 react with outrage when they’re singled out for blame.

Being a “wealth creator” means never having to say you’re sorry. Enough voters accept this proposition that Donald Trump paid no political price for unapologetic greed.

The worship of the marketplace, and thus the elevation of selfishness to a public virtue, is a doctrine that we associate with the libertarian right. But it has coursed through the culture as a self-justifying ideology for rich people of all political persuasions — perhaps also for people who merely dream of becoming rich.

Decadence is usually understood as an irreversible condition — the last stage before collapse.

The court of Muhammad Shah, last of the Mughals to control the entirety of their empire, lost itself in music and dance while the Persian army rode toward the Red Fort. But as American decadence is distinctive, perhaps America’s fate may be, too.

Even if it is written in the stars that China will supplant the United States as the world’s greatest power, other empires, Britain being the most obvious example and the one democracy among them, have surrendered the role of global hegemon without sliding into terminal decadence.

Can the United States emulate the stoic example of the country it once surpassed? I wonder.

The British have the gift of ironic realism. When the time came to exit the stage, they shuffled off with a slightly embarrassed shrug. That, of course, is not the American way. When the stage manager beckons us into the wings we look for someone to hit — each other, or immigrants or Muslims or any other kind of not-us.

Finding the reality of our situation inadmissible, like the deluded courtiers of the Shah of Iran, we slide into a malignant fantasy.

But precisely because we are a democracy, because the values and the mental habits that define us move upward from the people as well as downward from their leaders, that process need not be inexorable. The prospect of sending Roy Moore to the Senate forced a good many conservative Republicans into what may have been painful acts of self-reflection.

The revelations of widespread sexual abuse offer an opportunity for a cleansing moment of self-recognition — at least if we stop short of the hysterical overreaction that seems to govern almost everything in our lives.

Our political elite will continue to gratify our worst impulses so long as we continue to be governed by them. The only way back is to reclaim the common ground — political, moral, and even cognitive — that Donald Trump has lit on fire.

Losing to China is hardly the worst thing that could happen to us. Losing ourselves is.

James Traub is a contributing editor at Foreign Policy, a fellow at the Center on International Cooperation, and author of the book “John Quincy Adams: Militant Spirit.”[myad]