Just a few years ago, few of those outside the fledgling “alt right” movement had probably even heard of Breitbart, a site that seemed to specialize primarily in right-wing conspiracy theories. Now, former chairman Steve Bannon is a senior strategic adviser to President Trump, and the site’s reporters get preferential treatment from the White House.

Breitbart and other like-minded outlets didn’t single-handedly get Trump elected, but there has definitely been a symbiotic relationship between the two. In many ways, the rise of these right-wing alternative media and the rise of Donald Trump as a presidential candidate parallel each other, and they have arguably been fueled by similar undercurrents in U.S. society.

A new study from researchers with Harvard’s Berkman Center and MIT tracked the increasing influence of sites like Breitbart, the Daily Caller, Infowars and Truthfeed through the election. They researchers looked at more than a million news articles and the social-networking behavior around them to analyze the patterns that connect them.

While many Democrats and Trump critics are looking for external factors including Russian interference as an explanation for Trump’s victory, the study’s authors argue that this new media ecosystem arguably played an even larger role.

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“A right-wing media network anchored around Breitbart developed as a distinct and insulated media system, using social media as a backbone to transmit a hyper-partisan perspective,” the study says. “This pro-Trump media sphere appears to have not only successfully set the agenda for the conservative media sphere, but also strongly influenced the broader media.”

The study’s authors—including Yochai Benkler, a Harvard Law professor and co-director of the Berkman Center for Internet and Society; and Ethan Zuckerman of MIT’s Center for Civic Media—analyzed hyperlinks between different sites, social-sharing patterns on Facebook and Twitter, and the type of language used when sharing.

In all, the researchers mapped 1.25 million stories that were published by 25,000 different media outlets over the course of the election. They did this by using software called Media Cloud, an open-source platform co-developed by the Berkman Center and MIT’s Civic Media Center.

One of the core questions the study looked at was: “If a person shares a link from Breitbart, is he or she more likely also to share a link from Fox News or from The New York Times?”

The study’s analysis “challenges a simple narrative that the internet as a technology is what fragments public discourse and polarizes opinions,” the authors say. “If technology were the most important driver towards a ‘post-truth’ world, we would expect to see symmetric patterns on the left and the right.” But that wasn’t the case.

Instead, the analysis showed that while liberal or pro-Clinton users linked primarily to articles from mainstream news outlets, pro-Trump audiences spent almost all of their time linking to alternative sites like Breitbart, many of which didn’t even exist during the previous election.

Many of these outlets will no doubt argue that they didn’t pay any attention to mainstream media because the traditional press are all left-leaning. They will likely see the Harvard/MIT study data as confirming that belief — not to mention the fact that the study was financed by the Open Society Foundations. The OSF are funded by financier George Soros, a regular target of right-wing criticism.

In any case, what the insular nature of this alternative media ecosystem created, the authors say, was a self-reinforcing worldview shared by Trump supporters that was rarely challenged by fact-checking articles from outside the right-wing bubble. The Trump campaign clearly focused on catering to that worldview, and has continued to do so since he was elected.

Rather than just being “fake news,” many of the most-shared stories in this right-wing ecosystem “can more accurately be understood as disinformation,” the study says.

In other words, they represented “the purposeful construction of true or partly true bits of information into a message that is, at its core, misleading.” Over the course of the election, this turned the right-wing media ecosystem into what the authors call “an internally coherent, relatively insulated knowledge community, reinforcing the shared worldview of readers and shielding them from journalism that challenged it.”

Data journalism expert Jonathan Albright has also spent some time mapping the right-wing alternative media ecosystem, including the connections between fringe sites that were the largest channels for “fake news” reports during the election.

While the use of partisan agenda-driven media and disinformation tactics on both the left and the right isn’t new, Benkler and Zuckerman and their fellow researchers argue that the almost total insulation of right-wing media sources from the mainstream is “new and distinctive.”

What the media has to do now, the authors argue, is not try to fight this alternative ecosystem with better viral content or clickbait, but to “recognize that it is operating in a propaganda and disinformation-rich environment.” This is the primary challenge facing the press, they say, not Facebook—and rising to this challenge “could usher in a new golden age for the Fourth Estate.” How exactly the media should do this isn’t spelled out, however.