Editor’s Note: Nicole Hemmer is an associate research scholar at Columbia University and the author of “Messengers of the Right: Conservative Media and the Transformation of American Politics.” She hosts the history podcast “Past Present” and created the podcast “A12.” The views expressed in this commentary are solely those of the author. View more opinion articles on CNN. For more on the 1964 election, watch CNN Original Series “Race for the White House” Sundays at 9 p.m. ET/PT.

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Decades before President Donald Trump ever attacked the media, Senator Barry Goldwater introduced a new idea to the presidential campaign trail: liberal media bias.

Goldwater was 1964’s Republican presidential candidate, and he was convinced that the journalists covering the campaign were infusing their reporting with a left-leaning tilt while claiming to be neutral observers. As a staunch conservative, Goldwater believed this bias put him at a distinct disadvantage in his race against President Lyndon Johnson.

Nicole Hemmer

Struggling in the polls, he insisted that his message — rolling back the New Deal and taking the fight to the communists — was popular with Americans. The trouble, he said, was that his positions were constantly being distorted by the liberal gatekeepers in the media. He needled the journalists trailing him, even handing out pins to reporters that read “Eastern Liberal Press.”

Goldwater’s “liberal press” claim had some basis – television news broadcasts and major papers based on the coasts were staffed with journalists who personally tended to support at least some level of desegregation, social safety net programs and US cold war policy – but they weren’t the cause of his uphill battle with voters. Since the end of World War II, Republicans and Democrats had hashed out a rough consensus on many of the major issues of the day — a consensus Goldwater regularly rejected as he adopted positions well outside the mainstream.

It was his fringe position, not the press, that contributed to Goldwater’s loss in a historic landslide. Yet even in defeat, he’d pioneered an argument that would become a staple of Republican campaigns: the US media favored Democrats and liberals, and skewed their reporting to help their preferred candidate.

This argument wasn’t really true: many newspapers had a conservative bent, and most reporters maintained a commitment to the practice of objective journalism, regardless of their political preferences. But Goldwater discovered the political power of the bias charge, and future candidates would hone it into a brutally effective weapon – including Trump, who has used it as a key strategy throughout his presidency and will use it during his 2020 re-election campaign.

Goldwater was far from the first presidential candidate to complain about the press. In the 19th century, before the concept of objectivity became a journalistic norm, most newspapers were partisan. Criticizing papers for their political commitments made little sense — that was, after all, what newspapers were for from about 1790 through the late 1800s. In 1848, for instance, the Democrats and Whigs spent heavily to start newspapers just to circulate the party line. So despondent were the editors at the Republican Los Angeles Times after Democrat Grover Cleveland won the 1884 race, they simply refused to report the results for several days.

Even after objectivity became a journalistic practice in the early 20th century, presidential candidates still found plenty to criticize in the nation’s newsrooms – but the complaint was seldom that the papers were too liberal. In the 1930s, Franklin Roosevelt regularly railed against newspaper publishers, who he dubbed “press barons.”

He wasn’t wrong. Newspaper publishers often had a rooting interest in conservative presidential campaigns; one Republican president, Warren G. Harding, was himself a newspaper publisher. Henry Luce, who headed up a publishing empire including Time and Life magazines, pushed so hard for Republican Wendell Willkie in 1940 that one of his reporters cabled from the campaign train: “Take me off this train. All I can do is sit at the typewriter and write, ‘Wendell Willkie is a wonderful man. Wendell Willkie is a wonderful man.’”

For decades, this relationship between president and press was a state of affairs that rarely raised eyebrows among the public – until Goldwater’s 1964 campaign. With his complaints, he planted the seed for the now widespread belief among Republicans that the media is skewed to support the left, despite the reality at the time that many newspapers favored conservative Republicans.

He did this by tapping into already simmering pockets of resentment across the US; his “Eastern Liberal Press” pins were rooted as much in region as ideology. The senator hailed from Arizona, and long nurtured a disdain for the dominance of Eastern media, politics and culture.

And in the South, white-owned papers and television stations censored Northern coverage of the civil rights movement, and white southerners heatedly criticized Northern journalists for what they saw as pro-civil-rights bias.

This meant that by the time Goldwater became the presidential nominee, there was an audience more than ready for his message – one that had been arguing about journalism’s alleged left-wing bias for more than a decade. Hearing their arguments popularized by a presidential candidate was a boon to a movement that had operated on the fringes of the two major parties.

Cries of liberal media bias didn’t save Goldwater. But they did pave the way for a much more powerful criticism of American journalism five years later, when Richard Nixon entered the White House. Nixon was no stranger to lashing out at the press, but he tended to argue that journalists were anti-Nixon, not anti-conservative. It was his vice president, Spiro Agnew, who transformed Goldwater’s complaint into the one we recognize today: that a liberal coastal elite produces biased journalism that leaves the American people misinformed, hobbling their efforts to make wise political choices.

This tactic isn’t exclusive to conservatives – Sen. Bernie Sanders, who is running for the Democratic nomination, has suggested that The Washington Post’s coverage of his campaign is influenced by its ownership. But it is one that fueled the spread of a conservative media industry that remade American politics and journalism over the last 30 years. Belief in liberal media bias has become an article of faith on the right, a core part of conservative political identity.

In recent years, the idea has undergone another metamorphosis. Donald Trump, with his “fake news” slur, has charged something well beyond simply favoring one ideology over another. He’s accusing the media of wholesale fabrication – a line that, while completely untrue, delights his base.

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    Under Trump, the purpose of the media attack has become even more apparent: to delegitimize all news that isn’t subservient to him, while encouraging supporters to trust only one source — Donald Trump.

    Political journalism isn’t above criticism, far from it. But for the right, attacking the media is less about improving coverage or pointing out actual errors and biases, and more about eliminating alternative sources of information and rallying a base willing to ignore any news that comes from outside the movement.

    Understanding that strategy is vital to understanding the 2020 election. And it started with Barry Goldwater, more than a half-century ago.