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Here’s a test for measuring partisanship in American politics today: turn on C-SPAN and — without looking at the name of the lawmaker on screen — see how long it takes to tell whether the member of Congress is a Republican or a Democrat. Chances are high that you’ll figure it out in less than a minute.

Never before has American political speech been so partisan and polarizing, according to new research by Matthew Gentzkow, a senior fellow at the ��ɫApp Institute for Economic Policy Research.

Democrats today consistently use phrases like “undocumented workers” and “tax breaks for the wealthy,” while Republicans talk about “illegal aliens” and “tax reform.” After the June killing of 49 people at an Orlando nightclub, Democrats talked about a “mass shooting.” Republicans called it an act of “radical Islamic terrorism.”

The extent to which lawmakers’ speech reflects deep party divisions is unprecedented, according to Gentzkow’s research conducted with fellow economists Jesse Shapiro of Brown University and Matt Taddy of the University of Chicago Booth School of Business.

“The partisanship of language has exploded in recent decades,” said Gentzkow, a ��ɫApp economics professor. “The ways both parties use speech to promote their different visions is much different today than it was in the past.”

Gentzkow says his team’s findings — laid out in a  — have potentially profound implications, as political framing and language affect public opinion.

And it’s possible, he adds, that the starkly different languages Democrats and Republicans speak today is contributing to the hostility members of both parties harbor for one another.

“We know that language is a powerful driver of tribal identity,” said Gentzkow, “and tribal identities are getting stronger.”

Surprise discovery

The study examined speeches in the United States Congressional Record from 1872 to 2009. Gentzkow and his colleagues developed a machine-learning algorithm that analyzed 530,000 unique two-word phrases spoken 297 million times during that time period by Republicans and Democrats. Working its way through the first 135 years of data, the algorithm had about a 55 percent chance of correctly identifying whether one minute of a speech was uttered by a Democrat or a Republican.

The accuracy began improving dramatically based on speeches from 1994, when Republican congressmen started talking about a “Contract with America” that helped win them control of the House of Representatives in 1994. By the time the algorithm was crunching the most recently available data from 2008, it now registers an 83 percent chance of identifying the right party affiliation.

The results are striking. While other studies looking at signs of growing partisanship — mostly by counting congressional votes — have also seen a rise in recent decades, the increase has been gradual. They’ve also shown that the current level of partisanship is similar to the landscape earlier in the 20th century.

By comparison, the degree to which lawmakers began to pepper their speeches with party talking points changed almost overnight, in 1994.

“This was not at all what we expected to see,” said Gentzkow. At minimum, he and his colleagues predicted a strong correlation between legislative votes and increasingly partisan language in Congress.

Also, existing research into partisan speech had reached a different conclusion — showing that partisan language, while on the rise, was similarly prevalent in the past. But Gentzkow said the methodology used in his study improved upon past approaches and could potentially set a new standard for similar studies in the future.

A seminal moment

What, exactly, happened so dramatically in 1994? More than ever, Republicans began using focus groups, high-priced consultants and polling in a systematic way to identify language that resonated with voters and to coordinate messaging. The strategies were laid out by Newt Gingrich, then the House minority whip, and the political pollster and consultant Frank Luntz.

Soon, Democrats were following the same playbook.

The researchers note that the recent rise in partisanship isn’t because the topics of discussion have changed among Republicans and Democrats. They’re still talking about the same issues — immigration, crime, health care and taxes — but in an entirely new and highly coordinated way.

Even so, the introduction of savvy marketing into party politics doesn’t tell the whole story, said Gentzkow. C-SPAN and the rise of around-the-clock, partisan-leaning cable news shows may have given political leaders another reason to come up with a common narrative and rally party members to echo it.

“It seems very plausible that C-SPAN and cable television reinforced the parties’ increased sophistication in marketing,” said Gentzkow.

As Donald Trump and Bernie Sanders have seemingly pushed political rhetoric into even more divisive tones while ditching scripted talking points in favor of more spontaneous speeches, Gentzkow said it’s anybody’s guess whether Republicans and Democrats will stick to the language in their respective scripts.

“What will happen between 2010 to 2020? I can imagine the line (on a graph showing the steep rise in partisan speech) will keep going up and up,” Gentzkow said. “But I can also imagine it’s going to peak and come back down again because of voter backlash.”

Krysten Crawford is a freelance writer.