True, this is an idealized view. In the Trump era, many people avoid political talk with neighbors or family members they disagree with for fear of igniting bitter shouting matches.

And social learning is problematic when we only hang around with people who reinforce our own views and prejudices, as Bill Bishop suggested in his revelatory book, “The Big Sort.” Social media pushes us further into ideological silos, something Russian hackers understood in 2016.

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It ought to be the job of traditional media to help break this cycle. As Matthew Pressman shows in his recent history of journalism, “On Press: The Liberal Values That Shaped the News ,” there was a purpose behind the old ideas of “objectivity” and “fairness.” At their best, journalists examine questions of genuine importance and offer citizens a chance to hear competing arguments on various sides of the issues at stake. This task includes pointing out when claims are at odds with the facts.

Now only a naive rationalist would claim that politics is purely cerebral. It’s also about passion, self-interest and the foibles of would-be political leaders. But for democracy to work well, we need a balance among reason, emotion and interest. When reason is in retreat and when candidates are given strong incentives to stir up ugly passions, we have a problem.

This is where we are now, and President Trump is both the product of this crisis and its apotheosis. He brought home just how nonsensical and dishonest our politics have become with his assertion on Thursday about Mexico paying for his border wall: “Obviously, I never said this, and I never meant they’re going to write out a check.”

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This was shocking, even from an unrepentant liar. Trump denied ever saying something that, as David Nakamura reported in The Post, he did say “at least 212 times during his campaign and dozens more since he took office.”

This points to the media’s major shortcoming in 2016: its continuing commitment to “both sides are equally flawed” journalism, which led to its failure to portray Trump as the moral aberration he is. As Frank Bruni recently noted in the New York Times (citing the research of Harvard professor Thomas Patterson), treating Trump and Hillary Clinton “identically” in terms of their “fitness for office” was “madness.”

And as The Post’s media critic Margaret Sullivan noted, journalism needs to pull back from a “focus on personalities and electability” and on blowing gaffes “way out of proportion.” She endorsed New York University professor Jay Rosen’s idea that the press follow a “citizens agenda” in 2020. Why not more reporting on the problems that voters care about and how candidates propose to solve them?

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There are obvious responses to all this: Many voters knew who Trump was and voted for him anyway because they disliked Clinton even more; the critics just don’t like the way the election turned out; and many of our fellow citizens are so stuck in “media bubbles” that whatever mainstream journalism does won’t matter.

But whatever their merits, these assertions come down to a denial of responsibility. The mainstream media still greatly influence how we talk to one other about politics and should take this responsibility seriously.

Consider just two examples. A video of Rep. Alexandria Ocasio-Cortez’s collegiate dancing made for fun stories, but it’s far less important than the New York Democrat’s proposal for a 70 percent tax rate on incomes over $10 million. Coverage of Trump’s campaign-trail attacks against Jeb Bush for his “low energy” were a successful distraction from a serious conversation about Bush’s prophetic assertion that Trump would be a “chaos president.”

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None of this takes away from the fact that journalists still provide an abundance of accurate information. This includes, thank goodness, smart and tough coverage of Trump.

But Bruni, Sullivan, Patterson and Rosen are right to ask the media to ponder what role it has played in bringing our democracy to its current state. The arbiters of the news should be encouraging better conversations over those back fences — and doing a better job of warning us early on about politicians who lie even about their lies.