By Ms. Kakutani is a former book critic for The Times.

Two of the most widely quoted and shared poems in the closing years of this decade were William Butler Yeats’s “The Second Coming” (“Things fall apart; the centre cannot hold”), and W.H. Auden’s “September 1, 1939” (“Waves of anger and fear / Circulate over the bright / And darkened lands of the earth”). Yeats’s poem, written just after World War I, spoke of a time when “The best lack all conviction, while the worst / Are full of passionate intensity.” Auden’s poem, written in the wake of Germany’s invasion of Poland, described a world lying “in stupor,” as democracy was threatened and “the enlightenment driven away.”

Apocalypse is not yet upon our world as the 2010s draw to an end, but there are portents of disorder. The hopes nourished during the opening years of the decade — hopes that America was on a progressive path toward growing equality and freedom, hopes that technology held answers to some of our most pressing problems — have given way, with what feels like head-swiveling speed, to a dark and divisive new era. Fear and distrust are ascendant now. At home, hate-crime violence reached a 16-year high in 2018, the F.B.I. reported. Abroad, there were big geopolitical shifts. With the rise of nationalist movements and a backlash against globalization on both sides of the Atlantic, the liberal post-World War II order — based on economic integration and international institutions — began to unravel, and since 2017, the United States has not only abdicated its role as a stabilizing leader on the global stage, but is also sowing unpredictability and chaos abroad.

A 2019 Freedom House report, which recorded global declines in political rights and civil liberties over the last 13 years, found that “challenges to American democracy are testing the stability of its constitutional system and threatening to undermine political rights and civil liberties worldwide.”

If Lin-Manuel Miranda’s dazzling 2015 musical “Hamilton,” about the founders’ Enlightenment vision of the United States, embodied the hopes and diversity of America during the Obama years, dystopian fables and horror-driven films and television series — including “Black Mirror” (2016), a rebooted “Twilight Zone” (2019), “Joker” (2019), “Get Out” (2017), “Watchmen” (2019), “The Handmaid’s Tale” (2017) and “Westworld” (2016) — spoke to the darkening mood in the second half of the decade, as drug overdose deaths in America rose to nearly half a million by the decade’s end, life expectancy fell in the United States and Britain, and many of us started to realize that our data (tracking everything we viewed, bought and searched for online) was being sold and commodified, and that algorithms were shaping our lives in untold ways. In what was likely the hottest decade on record, scientists warned that climate change was swiftly approaching a “point of no return”; we learned that glaciers were melting at record speed at the top of the world; and fires ravaged California and Australia and threatened the very future of the Amazon rainforest.

Many of these troubling developments didn’t happen overnight. Even today’s poisonous political partisanship has been brewing for decades — dating back at least to Newt Gingrich’s insurgency — but President Trump has blown any idea of “normal” to smithereens, brazenly trampling constitutional rules, America’s founding ideals and virtually every norm of common decency and civil discourse.

The biggest casualty of the decade was trust. According to a Pew survey earlier this year, only 17 percent of Americans trust the government to do what is right “most of the time" or “just about always.” America’s reputation tumbled even further on the world stage: A 2018 Pew survey of 25 countries found that 70 percent of respondents said they lack confidence that the American president would make the right foreign policy moves. Between the end of President Barack Obama’s second term and late 2018, positive views of America fell 27 percentage points in Germany, 26 points in Canada, and 25 points in France. As with many things, Donald Trump is both a symptom and a radical accelerant of the decline in trust. While exploiting the anger at the establishment that snowballed around the world in response to the 2008 financial crisis, Mr. Trump has also cruelly amplified existing divisions and resentments in America, fueling suspicion of immigrants and minorities and injecting white nationalist views into the mainstream, in efforts to gin up his base.

Mr. Trump’s improbable rise benefited from a perfect storm of larger economic, social and demographic changes, and the profoundly disruptive effects of new technology. His ascent also coincided with the rising anxieties and sense of dislocation produced by such tectonic shifts. Around the world, liberal democracy is facing grave new challenges, authoritarianism is on the rise and science is being questioned by “post-fact” politicians. Echoes of Mr. Trump’s nativist populism can be found in Prime Minister Boris Johnson of Britain’s recent electoral victory and the Brexit referendum of 2016, and in the ascent of the far-right President Jair Bolsonaro of Brazil. Democracy is under threat in Hungary and Poland. Once fringe right-wing parties with openly racist agendas are rebranding themselves in Sweden and Belgium. And far-right groups in Germany and Spain are now the third-largest parties in those nations’ parliaments.

Illustration by The New York Times. Photograph by Doug Mills/The New York Times

At the same time, Donald Trump remains a uniquely American phenomenon. Although the United States was founded on the Enlightenment values of reason, liberty and progress, there has long been another strain of thinking at work beneath the surface — what Philip Roth called “the indigenous American berserk,” and the historian Richard Hofstadter famously described as “the paranoid style.”

It’s an outlook characterized by a sense of “heated exaggeration, suspiciousness, and conspiratorial fantasy,” Hofstadter wrote in his 1964 essay, and focused on perceived threats to “a nation, a culture, a way of life.” Its language is apocalyptic (Mr. Trump’s “American carnage” is a perfect example); its point of view, extremist. It regards its opponents as evil and ubiquitous, while portraying itself, in Hofstadter’s words, as “manning the barricades of civilization.”

The “paranoid style,” Hofstadter observed, tends to occur in “episodic waves.” The modern right wing, he wrote, feels dispossessed: “America has been largely taken away from them and their kind, though they are determined to try to repossess it.” In their view, “the old American virtues have already been eaten away by cosmopolitans and intellectuals,” and national independence has been “destroyed by treasonous plots, having as their most powerful agents not merely outsiders and foreigners but major statesmen seated at the very centers of American power.”

One well-known eruption of the “paranoid style” occurred in the 1950s with the anti-Communist hysteria led by Joseph McCarthy. It would surface again in the 1960s with the emergence on the national stage of George C. Wallace, who ran a presidential campaign fueled by racism and white working-class rage.

In his 2018 book “The Soul of America,” the historian Jon Meacham also wrote about the cycles of hope and fear in American history, emphasizing the role that presidents play in setting a tone for the country and defining — or undermining — its founding ideals. He wrote about presidents who have worked to unify the country and appeal to what Abraham Lincoln called “the better angels of our nature,” and those who have courted discord and division.

Lincoln was followed in office by his vice president Andrew Johnson, a champion of white supremacy who pardoned more than 7,000 Confederates and opposed the 14th Amendment. Johnson was impeached in 1868: And while he was not convicted in the Senate, the historian Brenda Wineapple argues, the House’s decision to impeach him implied “the glimmering hope of a better time coming, a better government, a fairer and more just one” down the road in the years to come.

Illustration by The New York Times. Photograph by Marcus Yam for The New York Times

Mr. Meacham notes that “extremism, racism, nativism, and isolationism, driven by fear of the unknown, tend to spike in periods of economic and social stress.” Periods, that is, like our own, when change of every sort is blowing across the globe.

The event that turned people’s sense of dislocation and disillusionment into populist anger on both the right (the Tea Party) and the left (Occupy Wall Street and, later, Bernie Sanders’s candidacy) was the 2008 financial crisis. Trust in government had been in sharp decline in previous decades — driven by Watergate and Vietnam in the 1970s, and more recently by the invasion of Iraq and the failure to find weapons of mass destruction there, and by frustration with worsening partisan gridlock in Washington. But the lingering fallout of the 2008 crash — growing income inequality, declining social mobility and dwindling job security — ignited rage against the elites and the status quo.

While the banks were bailed out and the fortunate 1 percent soon made back its losses (and more), working- and middle-class voters struggled to make up lost ground. Many students realized they were looking at jobs in the gig economy and years of crippling debt, while workers in the manufacturing sector found themselves downsized or out of work. As a candidate, Mr. Trump sold himself as the champion of such voters — whom he called “the forgotten men and women” — and he promised to “drain the swamp” in Washington. But once in office, he enlarged the swamp, hiring some 281 lobbyists, and set about cutting taxes for corporations and the very rich.

He also began a war on the institutions that were the very pillars of the government he now headed. In early 2017, Mr. Trump’s then adviser and strategist Steve Bannon vowed that the administration would wage a tireless battle for the “deconstruction of the administrative state” and the administration has done so ever since — nihilistically trying to undermine public faith in the efficacy, the professionalism, even the mission of the institutions that are crucial for guarding our national security, negotiating with foreign governments and ensuring the safety of our environment and workplaces. Mr. Trump also launched chilling attacks on those he reviled — from the F.B.I. to the judiciary — for having failed to put loyalty to him ahead of loyalty to the Constitution.

This is familiar behavior among authoritarians and would-be dictators, who resent constitutional checks and balances, and who want to make themselves the sole arbiters of truth and reality. A reporter said that in 2016 when she asked Mr. Trump why he continually assailed the press, he replied: “I do it to discredit you all and demean you all so when you write negative stories about me, no one will believe you.” It was fitting, then, that in January 2017, the month of his inauguration, George Orwell’s classic novel “1984” shot to the top of best-seller lists. The nearly 70-year-old novel suddenly felt unbearably timely with its depiction of a world in which the truth is whatever Big Brother says it is.

One of the terrible ironies of Mr. Trump’s presidency is that his administration’s dysfunction — little to no policymaking process on many issues, impulsive decision-making, contempt for expertise and plunging morale at beleaguered agencies — creates a toxic feedback loop that further undermines public trust in the government and lends momentum to his desire to eviscerate the “deep state.” The conflicts of interest that swirl around Mr. Trump and his cronies further increase the public’s perception of corruption and unfairness.

Illustration by The New York Times. Photograph by Lawrence Jackson for The New York Times

Meanwhile, tectonic shifts were occurring in technology: Not just game-changing developments in artificial intelligence, genetic research and space exploration, but also new platforms, apps and gadgets that almost immediately altered people’s daily habits, including Instagram (2010), Snapchat (2011), the iPad (2010), Uber (2009), and digital assistants Siri (2011) and Alexa (2014). In these years, we also developed a growing appreciation of technology’s dark side: Gamergate, N.S.A. surveillance, Russian attacks on our elections, the fear that you might not only lose your job to a stranger on the other side of the planet, but also to robots in your hometown.

In the 2010s, we also became addicted to podcasts, and binge-watching became a thing. In fact, immersion or escape into compelling fictional worlds seemed to be one strategy people were embracing to cope with political outrage fatigue. Perhaps this also explains why nostalgia became so popular in the 2010s with reboots and returns of old television shows like “Mad About You,” “Twin Peaks,” “The X-Files,” “Dynasty,” “Lost in Space,” “Roseanne,” “Will & Grace,” “Gilmore Girls” and “The Odd Couple” — a phenomenon that’s both a reflection of the retro-mania catalyzed by the endless availability of old content on the web and a longing for older, saner times.

With his calls to “Make America Great Again,” Mr. Trump appealed to a different sort of nostalgia — for an era when white men were in charge and women, African Americans, Hispanics and immigrants knew their place.

At the same time, Mr. Trump and his campaign revived the culture wars of the 1960s and ’70s, and politicized everything from football and Starbucks coffee cups (criticized by some evangelicals for being too secular and part of the “war on Christmas”) to plastic straws and windmills. It might have been funny if we were living in a satirical novel, not in the real world with a former reality TV star as president.

In his insightful forthcoming book, “Why We’re Polarized,” Ezra Klein observes that “our partisan identities have merged with our racial, religious, geographic, ideological, and cultural identities.” This is coming at a moment when the nation’s demographics are rapidly changing — census statistics project that America will become “minority white” in 2045 — and putting more emphasis than ever on questions of identity. Our political identities have become so crucial to us, Mr. Klein writes, that “we will justify almost anything or anyone so long as it helps our side, and the result is a politics devoid of guardrails, standards, persuasion, or accountability.”

It’s a measure of just how partisan our politics has become that most Republicans now reflexively support Mr. Trump — despite broken promises, ballooning deficits, and tariffs that have hurt Americans, never mind the astonishing volume of lies he emits. Many Trump supporters inhabit a soundproofed echo chamber: A 2017 study, published in the Columbia Journalism Review, found that pro-Trump audiences got most of their information from an insulated media system, anchored around Breitbart News, that reinforced “the shared worldview of readers” and shielded “them from journalism that challenged it.”

No surprise, then, that the president’s hard-core supporters stubbornly repeat the lies and conspiracy theories that cycle through his Twitter feed, connecting him with Russian trolls, white nationalists and random crackpots, or that Mr. Trump’s assertions and fictional narratives are amplified further by Republican politicians and the right-wing media noise machine.

Social media, which came into its own in the 2010s, accelerated the filter bubble effect further, as algorithms designed to maximize user “engagement” (and therefore maximize ad revenues) fed people customized data and ads that tended to reinforce their existing beliefs and interests. This is why Republicans and Democrats, conservatives and liberals, increasingly have trouble even agreeing upon shared facts — a development that has undermined trust between different groups, fueled incivility and sped up the niche-ification of culture that began years ago with the advent of cable television and the internet.

In addition, platforms like Facebook, Twitter and Instagram have enabled politicians (as well as advertisers, Russian agents and alt-right conspiracy theorists) to circumvent gatekeepers like the mainstream media and reach out directly to voters. “Influencers” replaced experts, scientists and scholars; memes and misinformation started to displace facts. As the news cycle spun faster and faster, our brains struggled to cope with the flood of data and distraction that endlessly spilled from our phones. And in an era of data overload and short attention spans, it’s not the most reliable, trustworthy material that goes viral — it’s the loudest voices, the angriest, most outrageous posts that get clicked and shared.

Without reliable information, citizens cannot make informed decisions about the issues of the day, and we cannot hold politicians to account. Without commonly agreed upon facts, we cannot have reasoned debates with other voters and instead become susceptible to the fear-mongering of demagogues. When politicians constantly lie, overwhelming and exhausting us while insinuating that everyone is dishonest and corrupt, the danger is that we grow so weary and cynical that we withdraw from civic engagement. And if we fail to engage in the political process — or reflexively support the individual from “our” party while reflexively dismissing the views of others — then we are abdicating common sense and our responsibility as citizens.

In his wise and astonishingly prescient “Farewell Address,” from 1796, George Washington spoke of the dangers he saw the young new nation facing in the future. He warned against “the insidious wiles of foreign influence,” “the impostures of pretended patriotism,” and, most insistently, of “the baneful effects of the spirit of party” — imploring his fellow citizens not to let partisan or geographic differences plant seeds of mistrust among those who “ought to be bound together by fraternal affection.”

Every portion of the country, he wrote, should remember: “You have in a common cause fought and triumphed together; the independence and liberty you possess are the work of joint counsels, and joint efforts of common dangers, sufferings, and successes.” Citizens, he urged, must indignantly frown “upon the first dawning of every attempt to alienate any portion of our country from the rest, or to enfeeble the sacred ties which now link together the various parts.”

Michiko Kakutani (@michikokakutani) is the author of “The Death of Truth: Notes on Falsehood in the Age of Trump.”

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