Last week, conservative radio, internet and television host Mark Levin published Unfreedom of the Press, an anti-media screed that debuted as Amazon’s No 1 bestseller, knocking Howard Stern’s memoir from the top spot.

Levin’s book attempts to reinforce a common argument: that the American “media”, which he writes about as if it were a single, monolithic entity, is hopelessly liberal in its world view, inexplicably invested in the success of the Democratic Party and therefore unworthy of the trust of Levin’s readers.

Unfreedom of the Press joins a centuries-old lineage of attacks on the American press, largely, but not exclusively, from the political right.

Thomas Jefferson, once a vocal supporter of newspapers, wrote to a young man during his presidency, “Nothing can now be believed which is seen in a newspaper. Truth itself becomes suspicious by being put into that polluted vehicle.”

But a crucial difference exists between the press in Jefferson’s era and the press that Levin harangues today. By the 20th century, the partisan press of Jefferson’s era had given way to a media that claimed to be driven by an ideal of objectivity. That premise has been the primary source of credibility for American journalists for most of a century.

Ironically, though, it is this claim to near-scientific neutrality that has opened the American press to attacks from the right for more than 50 years.

These attacks, in turn, have provoked a profound crisis of confidence in the system of reporting, one that threatens American democracy today.

Objectivity developed as a professional ideal in American journalism in the late 19th and early 20th centuries.

At the time, there was no, one “correct” model for journalism. But that began to change in 1896 when Adolph Ochs, who had just acquired The New York Times, declared that the paper would “give the news impartially, without fear or favour, regardless of party, sect, or interests involved.”

Gradually over the next 50 years, the commercial benefits of not choosing sides became clear (an impartial newspaper could sell subscriptions to Republicans and Democrats alike).

This spurred most mainstream outlets, large, general-circulation metropolitan daily newspapers, to embrace The New York Times as a model.

Professors in the journalism schools that began popping up in the early 20th century also adopted objectivity as a guide for the new set of professional norms their schools would teach.

By the time that radio, then television news, took hold, objectivity had become the standard rallying cry, with news anchors such as Walter Cronkite delivering a 22-minute picture of the world “as it was”.

Cronkite was never really the most trusted man in America, as the historian W. Joseph Campbell has pointed out, but the label stuck in a world where objectivity was the gold standard.

At the same time, the make-up of American newsrooms was changing. Before the Second World War, reporters were far likelier to have come from working-class families, making their way up through the newsroom ranks, although the top editors and publishers were generally college graduates.

After the war, this began to change, and by the end of the 1960s, young reporters who had been in college during the social upheavals of that decade began to chafe against the strict definitions of objectivity imposed by older editors. This frustration reflected a more general distrust of institutional authority. At The New York Times, David Halberstam challenged the statements of American generals in Vietnam and headed into the jungle to see the war for himself.

A few years later, his friend, J. Anthony Lukas, butted heads with editors who would not let him cover the trial of the Chicago Seven — activists who had led protests at the 1968 Chicago Democratic Convention — as a political show trial and insisted that he treat it as a criminal trial, just like the Government said it was.

The 1968 convention itself was a seminal moment that prompted a group of reporters to rethink the norm of objectivity. In a 1970 New York magazine article, the reporter and critic Edwin Diamond wrote that it “made many reflective journalists realise that they did have deep personal points of view”, something they should acknowledge.

Vice-President Spiro Agnew was among the first national politicians on the right to exploit the division between the mainstream press’s pose of objectivity and the clear viewpoints that were shaping journalists’ coverage.

Part of Agnew’s genius was to lump all reporters and news organisations into one vast, undifferentiated “media” that conspired to produce a twisted account of the news that little resembled the world as conservatives viewed it. This portrayal undermined confidence in the press more generally.

Books such as TV Guide writer Edith Efron’s The News Twisters, published in 1971, purported to analyse the leftward lean of the press with a scholarly veneer, and offered support for the administration’s move to undercut the media’s collective credibility. Dozens of books have followed in their wake.

In 1971, Lukas joined with colleagues to found (MORE), a journalism review that tried to nudge elite news organisations into a new set of practices and values for the press, ones that acknowledged, to some extent, the inherent subjectivity of news reporting. (MORE)’s goal was to leave journalism less susceptible to criticism like Agnew’s.

Interestingly, the staff of (MORE) included, for a time, the young reporter Brit Hume, who has become an ideological Fox News pundit.

The financial success that newspapers and broadcast television experienced in the 1980s papered over many of the arguments about objectivity that characterised the late 1960s and 1970s. This freed mainstream news organisations to continue the outward pose of neutrality that NYU journalism professor Jay Rosen calls “the view from nowhere”, a term borrowed from philosopher Thomas Nagel.

The failure to rethink this posture proved devastating in the internet era, as local newspapers began to fail and reporters became more concentrated in just a few American cities. This new geography of reporting revealed that the American press really does live in a sort of bubble. Follow some of the best reporters on Twitter today, and it’s easy to see how many of them know one another across institutions.

And so the cycle of the early 1970s is repeating itself. Smart but disingenuous critics like Levin — the successors of Agnew — pounce on the gap between purported objectivity and an obvious point of view to provoke a crisis of confidence in American journalism, one from which many of them profit handsomely as conservative media personalities.

However, their critique is often overly simplistic. The New York Times and The Washington Post are not liberal equivalents of Fox News. They are not partisan news outlets, nor in the employ of the Democratic Party.

Yet many of their reporters do share a world view. Most have university educations. Most live in large metropolitan areas on the East Coast, where they ride public transportation with people who aren’t like them, where there are large minority populations and LGBTQ neighbourhoods and restaurants serving Ethiopian food or regional Chinese — which they can probably get delivered to their apartments at midnight, when they’re still working on a story.

In short, the best journalists in the United States are in many ways more elite and more cosmopolitan than the American public in general. That, in and of itself, is not a bad thing.

Smart people who are aware of different kinds of life experiences make the best journalists. But that does mean that they have a particular way of seeing the world. And they would be much less susceptible to attacks from the Mark Levins of the world if they abandoned the pose of objectivity that opens them to those attacks.

• Kevin Lerner is an assistant professor of journalism at Marist College and author of Provoking the Press: (MORE) Magazine and The Crisis of Confidence in American Journalism