"They tend to discriminate, as when paying an opposing partisan less than a copartisan for identical job performance or recommending that an opposing partisan be denied a scholarship despite being the more qualified applicant," the study said.
Leveraging data from 1975 through 2017 in nine Western democracies -- Australia, Britain, Canada, Germany, New Zealand, Norway, Sweden, Switzerland and the United States -- the researchers found that by 2017 what they call "out-party hate" was stronger in the United States than in any other nation.
"The current state of political sectarianism produces prejudice, discrimination and cognitive distortion, undermining the ability of government to serve its core functions of representing the people and solving the nation's problems," said lead author Eli Finkel, a professor of social psychology at both Northwestern University's Weinberg College of Arts and Sciences and Kellogg School of Management, in a statement.
"Along the way, it makes people increasingly willing to support candidates who undermine democracy and to favor violence in support of their political goals," Finkel continued.
A frigid temperature
Americans have long felt affection for people who share their political views. On a "feeling thermometer" scale, where 0 degrees is cold, 50 degrees is neutral and 100 degrees is warm, feelings toward fellow Democrats or Republicans over the decades have consistently hovered in the 70-degree range.
Feelings toward people in the opposing party, however, plummeted from 48 degrees in the 1970s to 20 degrees today, the authors said.
"Things have gotten much more severe in the past decade, and there is no sign we've hit bottom," said coauthor James Druckman, a political science professor at the Institute for Policy Research at Northwestern, in a statement.
"As much as the parties differ from one another, partisans perceive even greater differences, believing, for example, that the other party is ideologically extreme, engaged and hostile," he added.
The study authors offer up three behaviors that lead to the increasingly frigid feelings. One is called "othering," which they define as the willingness to view the other side as essentially alien, and therefore completely different. The second they call aversion, which they call the tendency to "dislike and distrust" the opposite party. Finally, Americans are willing to consider people in the opposite party as grossly unfair and morally wrong.
"It is the confluence of these ingredients that makes sectarianism so corrosive in the political sphere. Viewing opposing partisans as different, or even as dislikable or immoral, may not be problematic in isolation. But when all three converge, political losses can feel like existential threats that must be averted — whatever the cost," the authors wrote.
Fanning the flames of dislike
In addition to a growing polarization of political identify, in which Republican politicians are moving further right and Democratic politicians further left, the study pointed to various forms of media as a catalyst for the growing chill.
To meet the FCC standards, broadcasters had a duty to understand a spectrum of views on any given issue and include experts best suited to representing those views in their programming.
Questions of constitutionality plagued the doctrine, and it was revoked in 1987. However, the removal of the doctrine helped lead to an explosion of conservative talk radio in the late 1980s and early 1990s, experts say.
"Among the first media figures to leverage the demise of the fairness doctrine was Rush Limbaugh, whose influential conservative radio program went into national syndication in 1988," the study authors wrote.
"The ethos of impartiality that CNN espoused when introducing cable news faltered with the launch of the conservative Fox News in 1996 and the liberal pivot of MSNBC a decade later," they wrote.
Social media may have helped fan the flames of distrust and polarization, the study said.
"Emotional and moralized posts — those containing words like 'hate,' 'shame,' or 'greed' — are especially likely to be retweeted within rather than between partisan networks," the study authors wrote.
In addition, "social-media technology employs popularity-based algorithms that tailor content to maximize user engagement, increasing sectarianism within homogeneous networks," they continued.
The role of those algorithms is the subject of a popular documentary entitled "The Social Dilemma," in which prominent leaders from Facebook, Twitter, Pinterest and others describe how they helped create algorithms which manipulate and shape our behavior.
For example, according to the film, "64% of the people who joined extremist groups on Facebook did so because the algorithms steered them there."
What to do?
Just fixing algorithms on social media platforms may not be enough, the authors said. They suggested encouraging people to deliberate about the accuracy of claims on social media, "which causes them to evaluate the substance of arguments and reduces their likelihood of sharing false or hyperpartisan content."
Perhaps crowdsourcing can be used to identify such content and the outlets that emit it, "relying on users' ratings of trustworthiness to augment the efforts of professional fact checkers."
Another solution is correcting inaccurate perceptions of our political opponents, the authors wrote.
"For example, Republicans estimate that 32% of Democrats are LGBT when in reality it is 6%; Democrats estimate that 38% of Republicans earn over $250,000 per year when in reality it is 2%."