There are very real — and substantial — policy differences separating the Democratic and Republican Parties. At the same time, what scholars variously describe as misperception and even delusion is driving up the intensity of contemporary partisan hostility.Matthew Levendusky, a political scientist at the University of Pennsylvania, describes some of these distorted views in his recently published book, “Our Common Bonds: Using What Americans Share to Help Bridge the Partisan Divide”:Seventy-five percent of Democrats said Republicans were closed-minded, and 55 percent of Republicans said that Democrats were immoral (Pew Research Center, 2019). Nearly eight in 10 say that the two parties “fundamentally disagree” about core American values. More than 70 percent of all voters think those in the other party are “a clear and present danger to the American way of life.”At an extreme level, James L. Martherus, Andres G. Martinez, Paul K. Piff and Alexander G. Theodoridis write in a July 2019 article “Party Animals? Extreme Partisan Polarization and Dehumanization,” “a substantial proportion of partisans are willing to directly say that they view members of the opposing party as less evolved than supporters of their own party.”In two surveys, the authors found that the mean score on what they call a “blatant difference measure” between Republicans and Democrats ranged from 31 to 36 points. The surveys asked respondents to rate members of each party on a 100-point “ascent of man” scale. Both Democrats and Republicans placed members of the opposition more than 30 points lower on the scale than members of their own party.“As a point of comparison,” they wrote, “these gaps are more than twice the dehumanization differences found by Kteily et al. (2015) for Muslims, 14 points, and nearly four times the gap for Mexican immigrants, 7.9 points, when comparing these groups with evaluations of ‘average Americans.’”A separate paper published last year, “Christian Nationalism and Political Violence: Victimhood, Racial Identity, Conspiracy and Support for the Capitol Attacks,” by Miles T. Armaly, David T. Buckley and Adam M. Enders, shows that support for political violence correlates with a combination of white identity, belief in extreme religions and conspiracy thinking.“Perceived victimhood, reinforcing racial and religious identities and support for conspiratorial information,” they wrote, “are positively related to each other and support for the Capitol riot.”Julie Wronski, a political scientist at the University of Mississippi, noted in an email that “much research has shown that Americans’ views of the other party are in fact driven by misperceptions and falsehoods.” Bringing Republicans and Democrats together and revealing their commonalities, she continued, “only lessens affective polarization. It cannot eliminate it.”Why?“Because humans are innately good at finding patterns and establishing stereotypes,” Wronski wrote, citing research showing that just as “Democrats overestimate the percentage of wealthy Republicans, Republicans overestimate the number of L.G.B.T.+ Democrats.”Since these beliefs have their foundations in core values, self-image and group identities, Wronski wrote, “people are motivated to defend them. Protecting your identity becomes more important than embracing the truth.”In other words, misperceptions and delusions interact dangerously with core political and moral disagreements.In March 2021, Michael Dimock, the president of the Pew Research Center, published “America Is Exceptional in Its Political Divide,” in which he explored some of this country’s vulnerabilities to extreme, emotionally driven polarization:America’s relatively rigid, two-party electoral system stands apart by collapsing a wide range of legitimate social and political debates into a singular battle line that can make our differences appear even larger than they may actually be. And when the balance of support for these political parties is close enough for either to gain near-term electoral advantage — as it has in the U.S. for more than a quarter century — the competition becomes cutthroat, and politics begins to feel zero-sum, where one side’s gain is inherently the other’s loss.At the same time, Dimock continued:Various types of identities have become ‘stacked’ on top of people’s partisan identities. Race, religion and ideology now align with partisan identity in ways that they often didn’t in eras when the two parties were relatively heterogenous coalitions.The result is that an individual whose party loses on Election Day can feel that his or her identity has suffered a defeat.In separate analyses, Pew has demonstrated the scope of mutual misperception by Democrats and Republicans. In an August 2022 study, “As Partisan Hostility Grows, Signs of Frustration With the Two-Party System,” Pew found that majorities of both parties viewed the opposition as immoral, dishonest, closed-minded and unintelligent — judgments that grew even more adverse, by 13 to 28 points, from 2016 to 2022. In a June-July 2022 survey, Pew found that 78 percent of Republicans believed Democratic policies are “harmful to the country” and 68 percent of Democrats held a comparable view of Republican policies.I asked Robb Willer, a sociologist at Stanford, about these developments, and he emailed back, “Americans misperceive the extent of policy disagreement, antidemocratic attitudes, support for political violence, dehumanization of rival partisans — again with the strongest results for perceptions of the views of rival partisans.”Importantly, Willer continued, “misperceptions of political division are more than mere vapor. There is good reason to think that these misperceptions — or at least Democrats’ and Republicans’ misperceptions of their rivals — really matter.”Why?Democrats and Republicans don’t want to bring a knife to a gunfight; they greatly overestimate how much their rivals want to break norms of nonviolent, democratic engagement, and this leads Democrats and Republicans to support violent and undemocratic engagement more than they otherwise would.He concluded:As the old sociological adage goes, situations believed to be real can become real in their consequences. It is likely that Democrats’ and Republicans’ inaccurate, overly negative stereotypes of one another are to some extent self-fulfilling, leading partisans to adopt more divisive, conflictual views than they would if they saw each other more accurately.Willer and others who described the centrality of misperception in American politics stressed that they do not want to diminish the serious divisions between Democrats and Republicans on such matters as abortion, race, women’s rights, the safety net and the proper role of government.Lilliana Mason, a political scientist at Johns Hopkins and the author of “Uncivil Agreement: How Politics Became Our Identity,” stressed these points in an emailed response to my questions, saying, “Democrats and Republicans are having very real and consequential disagreements on matters of equality, social hierarchy and what it means to be American.”At the same time, Mason continued:Matters of status and identity are easy to whip up into existential conflicts with zero-sum solutions. To the extent that political leaders are encouraging people to focus on threats to their social status rather than their economic or material well-being, they are certainly directing attention in an unhelpful and often dangerous direction. It’s much easier to think of others as disproportionately dangerous and extreme when their victory means your loss, rather than focusing on the overall well-being of the nation as a whole.Alia Braley, a doctoral candidate in political science at the University of California, Berkeley, is the lead author of an August 2022 paper, “The Subversion Dilemma: Why Voters Who Cherish Democracy Participate in Democratic Backsliding.” She and her co-authors argued that “simply fearing that opposing partisans support democratic backsliding can lead individuals to support it themselves.”In an email, Braley wrote:We find that everyday Democrats believe that everyday Republicans are way more hostile to democracy than they really are. And vice versa. In that sense people are, in fact, operating under a delusion that everyday opposing partisans are willing to undermine democracy. And yes, this misperception seems to cause intense affective polarization.Partisans, Braley continued, “overestimate how much members of the other party dislike and dehumanize them. Partisans tend to believe members of the other party want far more extreme policy outcomes than they actually do.” These misperceptions “can create a type of downward spiral in terms of polarization,” she wrote, citing Donald Trump’s claim that the 2020 election was stolen:This rhetoric likely causes Republicans to start to believe that Democrats are undermining democracy. When Democrats see this election denial, they naturally come to think that Republicans are trying to undermine democracy by not accepting election results. The result is a state of mutual fear.Gabriel Lenz — a political scientist at Berkeley and one of Braley’s co-authors — emailed to say “that much of the polarization is delusional.”“There are two main drivers” of this phenomenon, Lenz wrote. The first “is the need for politicians to mobilize citizens with busy lives and not much of an incentive to participate in politics. There are many ways politicians can mobilize voters, but fear is tried and true.”The second is speculative: “That humans evolved to survive conflict with the other human groups around them,” Lenz wrote. “This likely selected for people who excelled at sticking together in conflicts. Many of our biases seem explained by this incentive, especially a tendency to see the other side as evil.”Lenz stressed the point thatPoliticians don’t need to fully convince their supporters of these perceptions to get their supporters to act on them. If I’m only partially convinced that Democrats intend to steal the next election or want to murder babies, that partial belief may still be enough to get me to act.Even more significant, according to Lenz, is the recognition thatSome misperceptions are much more important than others. Misperceptions on policy or on the demographic makeup of parties are probably important, but they don’t directly threaten democracy. Misperceiving that the other side no longer supports democracy, however, is a more direct threat to democracy. It’s a more direct threat because it leads your own side to no longer support democracy to the same degree.Lenz cited a 2020 paper, “Malice and Stupidity: Out-Group Motive Attribution and Affective Polarization” by Sean Freeder, a political scientist at the University of North Florida, who argued that “negative motive attribution — partisans’ tendency to assume ill intent guides out-party interests” is a “key dynamic underlying affective polarization. When asked why out-party members prefer certain policy outcomes, roughly half of partisan respondents offer an explanation involving selfishness, ignorance, hatred and other negative motives.”Freeder wrote:Exposure to positive out-group motives does appear to lead respondents to update out-partisan attributions, which in turn leads to increased out-group affect. However, motivated reasoning makes such updating likely only when the out-party motives shown are of uniformly high quality — even one bad apple appears to spoil the whole bunch.Affective polarization can, in Freeder’s analysis, take on a momentum of its own:Once partisan polarization begins, negative motive attribution may provide partisans with an easy way to ‘other’ the out-group, which in turn increases the internal desire to further negatively attribute. Such a feedback loop leads citizens to perceive themselves as increasingly surrounded by monsters.There are other problems with efforts to lessen the mutual disdain of Democrats and Republicans.A May 2023 paper by Diego A. Reinero, Elizabeth A. Harris, Steve Rathje, Annie Duke and Jay Van Bavel, “Partisans Are More Likely to Entrench Their Beliefs in Misinformation When Political Out-Group Members Fact-Check Claims,” argued that “fact-checks were more likely to backfire when they came from a political out-group member” and that “corrections from political out-group members were 52 percent more likely to backfire — leaving people with more entrenched beliefs in misinformation.”In sum, the authors concluded, “corrections are effective on average but have small effects compared to partisan identity congruence and sometimes backfire — especially if they come from a political out-group member.”The rise of contemporary affective polarization is a distinctly 21st-century phenomenon.In a July 2022 paper, “Testing the Robustness of the ANES Feeling Thermometer Indicators of Affective Polarization,” Shanto Iyengar and Matthew Tyler, both political scientists at Stanford, found thatThe share of American National Election Studies partisans expressing extreme negativity for the out-party (a rating of 0 on a scale of 0 to 100) remained quite small leading up to and during 2000. Since 2000, however, the size of this share has increased dramatically — from 8 percent in 2000 to 40 percent in 2020. Thus, over the first two decades of this century, partisans’ mild dislike for their opponents metastasized into a deeper form of animus.In their paper “Partisan Gaps in Political Information and Information-Seeking Behavior: Motivated Reasoning or Cheerleading?” Erik Peterson, a political scientist at Rice, and Iyengar asked, “Do partisan disagreements over politically relevant facts and preferences for the information sources from which to obtain them represent genuine differences of opinion or insincere cheerleading?”Their answer: “Overall, our findings support the motivated reasoning interpretation of misinformation; partisans seek out information with congenial slant and sincerely adopt inaccurate beliefs that cast their party in a favorable light.”In an email, Iyengar warned that “The threat to democratic functioning posed by misinformation is real. The people who stormed the Capitol were not cheerleading; they genuinely believed the election was ‘stolen.’”He wrote that of the causes of increased affective polarization, “the explanation I consider most viable is changes in the media environment.” In the 1970s, he continued, “the vast majority of the voting-age population encountered the same news stories on the same topics” — what he called “a vast information commons.”Today, Iyengar wrote, not only are there more sources of information, but also “partisans have ample opportunity to tune in to ‘congenial sources’ — news providers delivering coverage with a partisan slant in accord with the viewer.”Nathaniel Persily, a law professor at Stanford, wrote by email that “there are two schools of thought” concerning delusions and misperceptions in contemporary politics:The first argues that factual mistakes are a significant engine of polarization and if we spend time correcting people’s misperceptions, it will have beneficial knock-on effects in reducing affective polarization.He continued, “In lab settings or other controlled environments where experts can bombard subjects with accurate information, people can move toward the center and release themselves from some of their partisan misconceptions.”Persily wrote, however, that his analysis falls into a second school of thought:I do not think most of affective polarization is driven by a misunderstanding of facts. Indeed, I think many in this field make the mistake of thinking that the line to be policed is the line between truth and falsehood. Rather, I think the critical question is usually whether the truth is relevant or not.In this context, according to Persily, “partisan polarization resembles religious polarization. Attempting to ‘disprove’ someone’s long-held religion will rarely do much to convince them that your god is the right one.”Viewed this way, partisan affiliation is an identity, Persily wrote, “and displays dynamics familiar to identity politics”:People root for their team, and they find facts or other narratives to justify doing so. Remember, most people do not spend a lot of time thinking about politics. When they do so, their attitudes grow out of other affinities they have developed over time from signals sent by trusted elites or friendship networks.Jay Van Bavel, a professor of psychology and neural science at N.Y.U., shares Iyengar’s view on the key role of the changing media environment. In an email, he wrote:A good chunk of affective polarization is delusion or based on misperceptions. For instance, people have exaggerated stereotypes about the other party (and what members of the other party think of them), and when you correct those false perceptions, they quickly become less hostile.People are motivated, he continued,to affirm evidence that confirms their beliefs and affirms their identities. For committed partisans, they are often more motivated by these social goals than the desire to be accurate. People also share misinformation for social reasons — it can signal loyalty and help people gain status in some partisan communities.A significant component, Van Bavel said, “is based on misperceptions they’ve absorbed from their social network on (social) media stories. It suggests that if we could simply provide accurate and diverse portrayals of other groups, it might reduce the growing trend toward affective polarization.”But, he cautioned, “correcting misinformation is extremely hard; the impact tends to be pretty small in the political domain, and the effects don’t last long.”In a 2021 paper, “Identity Concerns Drive Belief: The Impact of Partisan Identity on the Belief and Dissemination of True and False News,” Andrea Pereira, Elizabeth Harris and Van Bavel surveyed 1,420 Americans to see which of the following three alternatives best explained the rise and spread of political misinformation:The ideological values hypothesis (people prefer news that bolster their values and worldviews), the confirmation bias hypothesis (people prefer news that fit their pre-existing stereotypical knowledge) and the political identity hypothesis (people prefer news that allow them to believe positive things about political in-group members and negative things about political out-group members).Their conclusion:Consistent with the political identity hypothesis, Democrats and Republicans were both more likely to believe news about the value-upholding behavior of their in-group or the value-undermining behavior of their out-group. Belief was positively correlated with willingness to share on social media in all conditions, but Republicans were more likely to believe and want to share political fake news.There have been a number of studies published in recent years describing the success or failure of various approaches to reducing levels of misperception and affective polarization. The difficulties facing these efforts are reflected, in part, in an October 2022 paper, “Interventions Reducing Affective Polarization Do Not Necessarily Improve Antidemocratic Attitudes,” by Jan G. Voelkel, a sociologist at Stanford, and eight colleagues.The authors found that even when “three depolarization interventions reliably reduced self-reported affective polarization,” the interventions “did not reliably reduce any of three measures of antidemocratic attitudes: support for undemocratic candidates, support for partisan violence and prioritizing partisan ends over democratic means.”In other words, the irrational element of partisan hostility has seemingly created a political culture resistant to correction or reform. If so, the nation is stuck, at least for the time being, in a destructive cyclical pattern that no one so far has found a way to escape.The embodiment of delusional politics is, of course, Donald Trump, with his false, indeed fraudulent, claim that the 2020 election was stolen from him. The continuing willingness of a majority of Republican voters to tolerate this delusion reflects the difficulty facing the nation as it struggles to restore sanity to American politics — if it’s not too late.The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips. And here’s our email: letters@nytimes.com.Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram. More