John Avlon is a CNN senior political analyst. The opinions expressed in this commentary are his own. View more opinion articles on CNN.

(CNN) America is self-segregating into separate political realities. And partisan media is driving much of this division across new platforms, polarizing for profit while amplifying extreme voices and achieving unprecedented reach -- including the Oval Office.

President Donald Trump is a creature of partisan media, having kicked off his political career with regular appearances on Fox News. His obsessive consumption causes him to echo its talking points , often overriding information from US intelligence agencies. This leaves him susceptible to conspiracy theories that have now led to the fourth impeachment inquiry in our history.

We've always had partisan media in America, with Alexander Hamilton and Thomas Jefferson slashing each other in the pages of competing broadsheets on the same street in Philadelphia.

What we're dealing with today is different because of the pervasive scale of partisan media and its dissemination alongside disinformation. Its proliferation has been hastened by the rise of a partisan economy amid a fragmented media market, aiming to keep a narrow but intense niche audience addicted to anger, anxiety and resentment. But this is a Faustian bargain, because it requires going to ever-increasing extremes to keep the audience engaged while constantly attacking the credibility of nonpartisan news organizations.

The rise of social media has balkanized us further , amplifying the loudest voices, often manipulating perceptions of public opinion via anonymous bots and trolls, while driving many reasonable people from the public square of civic debate. These disinformation deployments often shape the tone of partisan media while exploiting the lack of trust it has helped create.

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The result is real: A new Pew Survey shows that 73% of Americans now believe that Republicans and Democrats cannot agree on basic facts. That's a potential death sentence for a democracy that depends on reasoning together to solve common problems.

This is also an unhealthy departure from our best traditions. We had partisan newspapers in the past that, for example, excoriated and defended the New Deal, but there was still a general baseline commitment to facts and a clear delineation between news and editorial opinion. On the broadcast side, the fairness doctrine, introduced in 1949, was a condition of leasing federal airwaves that aimed to ensure balance by requiring time for opposing political views.

That doesn't mean there were not deep disagreements and bitter debate.

The Joe McCarthy test

America was tested by the rise of Sen. Joe McCarthy of Wisconsin, a conservative, populist anti-communist with a demagogue's disregard for facts. While accusing Democrats of treason, McCarthy often tried to play the victim of the liberal elite media , equating The Washington Post with the communist Daily Worker -- while in fact old-line Republican papers like the Chicago Tribune and New York Herald Tribune were also warning about McCarthy's tactics.

McCarthy's rise on the back of wild accusations caused some editors to question whether the traditional approach of simply reporting what a public official said was consistent with the larger responsibility of telling the truth. But McCarthy met his match in Edward R. Murrow, the legendary CBS broadcast news pioneer, who took on McCarthy by fact-checking his public statements, closing his show in March 1954 by saying , "We must not confuse dissent with disloyalty. ... We will not be driven by fear into an age of unreason."

But Murrow vs. McCarthy was a notable exception in a post-war period. Despite the stickiness of who was determining what was fair and balanced, the fairness doctrine proved surprisingly popular among conservatives and liberals who believed it ensured a degree of "public interest" programming. When it was overturned by the Federal Communications Commission in 1987, the Senate voted 59-31 to reinstate it on bipartisan lines -- but it was vetoed by former President Ronald Reagan.

This is when partisan media as we know it began to proliferate.

From the fairness doctrine to Fox News

One study by former chief economist at the FCC Thomas Winslow Hazlett, recounted in his book " The Political Spectrum ," found that talk radio took off after the fairness doctrine was dismantled, displacing what had been the most popular radio format: music. Our country got more polarized as partisan opinion became big business, untethered from any obligation to be fair and balanced.

This was the moment Roger Ailes had been waiting for. A one-time talk show producer-turned-political consultant, Ailes pushed a political strategy called "positive polarization" in Richard Nixon's 1968 presidential campaign. While Nixon repeated "the press is the enemy" like a mantra, Ailes envisioned the creation of a conservative news network that could counteract major newspapers and the big three networks.

Ailes had the opportunity to operationalize his partisan dream with the launch of Fox News in 1996. Extending the popularity of right-wing talk radio into cable news, the idea was simple and sinister: Only explicit bias could balance the implicit bias of the mainstream media. But in a breathtaking bit of cynicism, this partisan project would be sold as " fair and balanced ."

Later that same year, MSNBC launched and evolved into a liberal counterweight. The partisan media arms race was on. But what is good for ratings can be bad for the country.

Partisan media and the decline of trust

The impact was clear: Just over a decade later, a Pew Survey on media credibility found that "virtually every news organization or program has seen its credibility marks decline." Even C-SPAN, which offers unedited coverage of public events, experienced a steep decline in believability. In this hyper-partisan environment, people literally weren't trusting what they see with their own eyes.

Instead of creating more informed citizens, partisan media compounded tribalism through an echo chamber -- a loose network of blogs, talk radio and partisan cable news that mainstreamed conspiracy theories and increasingly gave talking points to party leaders rather than vice versa.

Then came social media. It promised to break down barriers, but instead of simply being a great leveler, it was quickly hijacked by operatives who realized that it was also the greatest vehicle for disinformation ever devised.

The Trump effect

All these dynamics contributed to the rise of Donald Trump to the presidency. He took his reality television celebrity and morphed it into political influence with weekly segments on "Fox and Friends," where he started peddling the birther conspiracy theory that former President Barack Obama was ineligible to be president.

But it was his use of Twitter to hijack news cycles with outrageous statements that really boosted his presidential campaign. What Trump understood better than most is that news doesn't have a liberal or a conservative bias as much as a conflict bias -- and he supplied constant conflict in ways that fired up his base while dominating news cycles on stations and sites across the political spectrum.

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The Republican establishment couldn't stop his rise, because the conservative base had become radicalized by hyper-partisan media while many on the center-right had opted out of the party.

It was a joint effort. During the 2016 campaign, Trump relied on regular strategic conversations with Ailes and Sean Hannity, while bringing on the former head of Breitbart News, Steve Bannon, to run his campaign. Put simply, Trump promoted hyper-partisan media, and they promoted him in return.

On the most extreme edge, we even learned that the campaign's senior policy adviser, Stephen Miller, was back-channeling with Breitbart to influence their immigration coverage with white nationalist sites. On a far more prominent and less fringe scale, The Washington Post's Erik Wemple chronicled Hannity's many mentions in campaign emails and called him their "chief propagandist ... looped in on all their talking points, their deflections and their innumerable attacks."

During the final weeks of the campaign, when few even inside Trump's orbit believed he could win, Trump was musing about starting his own right-wing television station -- Trump TV -- to be led by none other than Ailes. It would allow him to monetize the movement he'd begun while continuing its momentum based on the idea that the election had been stolen.

But trolls and bots on social media -- many of them connected to Russia -- were engaging in an all-out final push to try to elect Trump, exploiting the environment of extremism and distrust that partisan media created, posting intentionally fake stories at an accelerated rate. In the final three months of the campaign, the top performing intentionally false stories on Facebook -- designed to benefit Trump and hurt Hillary Clinton -- out-performed the top news stories from actual publications, according to the bipartisan Senate Intelligence Committee report.

The top two fake news stories were Pope Francis' (non-existent) endorsement of Trump and Wikileaks' "confirmation" of Hillary Clinton's weapons sales to ISIS -- which reached more than 1.7 million people. One analyst explained that "it seems pretty clear that false information outperforms true information."

President-elect Trump quickly tried to twist the term "fake news" -- which helped him win the election -- to refer to any independent journalism that displeased him in any way. He has used the term more than 1,100 times since inauguration, according to Factba.se, while autocrats around the world approvingly picked up the term.

Partisan media was in the White House, and Trump's relationship with Fox News became something unseen in American history -- with the President constantly watching and tweeting out promos to friendly shows while hiring more than 20 administration aides from the extended Fox talent pool.

When his staffers burnt out or were forced out, they often found jobs at Fox -- while a few lonely correspondents and anchors such as Shepard Smith committed to facts found themselves under fire from viewers as well as the President.

"I've never seen anything like it before," Fox News president-turned-NYU journalism professor Joe Peyronnin told The New Yorker's Jane Mayer . "It's as if the President had his own press organization. It's not healthy."

Partisan media takes over the White House

We see that partisan media has completed its takeover of the White House -- electing and bolstering an unpopular President while perpetuating a separate political reality for his supporters. But there is a cost to living in that closed environment.

The fourth impeachment inquiry in American history was launched because Trump bought into discredited conspiracy theories that Ukraine -- not Russia -- had hacked the Democratic National Committee while pushing that country's new President to investigate the family of his chief political rival. These ideas were allegedly spread from interested parties and fringe sites to being investigated by Trump's personal attorney, Rudy Giuliani -- who fed information to The Hill's John Solomon -- whose articles created "evidence" used to justify the investigation. Solomon would in turn promote his stories on Hannity's show on Fox News -- creating a confirmation bias feedback loop built on falsehoods, or what the President's supporters might call "alternative facts."

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The media coverage of the subsequent impeachment inquiry hearings was also polarized, with one side focused on testimony and facts, while the other side attacked the State Department and White House witnesses as "Never Trumpers," " nerdy guys ," "radicals," "partisan bureaucrats" and even a " self-important, very narcissistic diplomatic snowflake ." There's an inability to agree on basic facts, and instead the politics of personal attacks seem to have aligned with the President's talking points.

Confronting an age of unreason

There's no question that partisan media has driven the polarization that's afflicting our nation. It is driving the agenda in the White House. And proximity to power creates a gravitational pull toward normalization.

But the partisan echo chamber is a route to radicalization. As Cass Sunstein explains in his book "Going to Extremes," "A good way to create an extremist group, or a cult of any kind, is to separate members from the rest of society. The separation can occur physically or psychologically, by creating a sense of suspicion about non-members. With such separation, the information and views of those outside the group can be discredited, and hence nothing will disturb the process of polarization as group members continue to talk."

Partisan media has gone from advancing an ideological agenda to something uglier, something like a cult that is peddling special knowledge -- undermining our ability to reason together as Americans, while sharpening tribal divides.