They had been on the air for more than 10 hours, crammed against one another along a single desk, phone cords coiled across their scraps of wire copy, three anchormen stunned, yet in their element.

Frank McGee, Bill Ryan and Chet Huntley read bulletins, fielded calls and calmed the NBC reporters who were trying to do what no one had ever done before: cover a national trauma in real time on live television, leading an unprecedented gathering of Americans through the initial jolt, the ensuing grief, and a strange new sense of watching and mourning together.

Finally, the dark day in Dallas eased into a new presidency’s first morning, and the director switched to David Brinkley in Washington, who pulled back from the frenetic hunt for shreds of information:

“It has all been shocking,” he said in his trademark, deliberate staccato, “but perhaps one element in the shock was the speed.” At 1 p.m. on that November afternoon in 1963, “President Kennedy was about as alive as any human being could ever get — young, strong vigorous. . . . His wife, young, beautiful and looking very happy, was beside him. . . .

“Five hours later . . . Mr. Kennedy had been murdered. Lyndon Johnson was president of the United States. Mrs. Kennedy was a widow, a brave and composed one that nobody could fail to admire. All of them were back in Washington. . . .The sheer speed of it was just too fast for the senses.”

To Brinkley, then 43, the immediate comparison was to the death of Franklin D. Roosevelt just 18 years earlier. The news back then traveled by newspaper and radio, with none of the live pictures and nonstop accompaniment that the three networks improvised for four days after Lee Harvey Oswald fired his $12 mail-order rifle from the sixth floor of the Texas School Book Depository. In 1945, everybody had “time to think about what had happened,” Brinkley said. “There is seldom any time to think anymore, and today there was none.”

The Kennedy assassination brought shock and speed, and as novelists, poets, filmmakers and the town criers of the American night have portrayed it over the past 50 years, the trauma resulted in lost moorings, frayed relationships and diminished trust.

“What has become unraveled since that afternoon in Dallas,” the novelist Don DeLillo wrote in 1983 in Rolling Stone, “is the sense of a coherent reality most of us shared. We seem from that moment to have entered a world of randomness and ambiguity,” a time of “estrangement and silence.”

Ever since Kennedy was killed, the writer Norman Mailer once said, “we have been marooned in one of two equally intolerable spiritual states, apathy or paranoia.”

But if the assassination felt like a passage into a time of wilting standards and hazier values, efforts to prove that the murder actually twisted the course of the nation have mainly produced fuzzy results — except in the case of how Americans experience public trauma.

Academics tracked every possible indicator of social, economic and political health. The popularity of extremist political movements declined considerably in the period after the assassination, says Michael Kurtz, a historian at Southeastern Louisiana University. An epidemic of conspiracy theories blossomed, but such skepticism about the official story was hardly new. Americans’ weakness for alternative histories goes back to revolutionary times, when Colonial leaders interpreted a series of British acts as a deliberate effort to limit the freedom of Americans and prepare for dictatorship.

Violent crime spiked sharply in U.S. cities after the assassination, just as it did after Richard Speck killed eight nurses in Chicago in 1966 and after Charles Whitman climbed a tower on the University of Texas campus and shot 45 people later that same summer.

But most studies concluded that the killing of Kennedy, by itself, didn’t explain the unrest and upheaval of the late ’60s and early ’70s.

What did produce lasting change was the four days of round-the-clock coverage — “the birth of a new media culture,” says Aniko Bodroghkozy, a communications professor at the University of Virginia who has studied the impact of the Kennedy murder.

TV, which had in recent years become a standard appliance in American homes, asserted itself as the nation’s primary source of news. The three networks had expanded to half-hour nightly newscasts just two months before the shootings in Dallas. The idea that TV broadcasters might stay on the air all night was itself a novelty born of the assassination.

In the unscripted marathon that carried the nation from fragmentary bulletins to the long vigil with cameras trained on the casket in the Capitol Rotunda, TV became the national commons, attracting a record 96 percent of U.S. households, uniting people in trauma and grief.

“We were so far away, but yet so near,” a viewer in LaGrande, Ore., wrote to NBC’s Huntley in a letter Bodroghkozy found in Huntley’s papers. “The television brought us there and we felt very much a part of everything. We were able to go into the church & see & hear the sermon.”

“Had we been there, we would have been just two John Does,” wrote a couple from Elmira, Ore., “but by the medium of television we had the feeling of dignitaries because we were there.”

This sense of feeling like a participant was a common theme in hundreds of letters Bodroghkozy examined. National traumas from then on would be shared in the moment, across the continent, through a video screen.

This experience unsettled some — one letter writer compared it to “witchcraft” — and comforted others. But everyone seemed affected by TV’s emotional intimacy. Even as the anchormen maintained a professional seriousness, the occasional catch in McGee’s voice, the wince on Walter Cronkite’s face, the way Brinkley spoke directly to viewers — it all spotlighted a new relationship between the people and the events that shaped their country.

Kennedy himself had seen this coming. In 1959, when TV was so new that people debated whether candidates should advertise on the medium, then-Sen. Kennedy wrote in TV Guide that television revealed a candidate’s “honesty, vigor, compassion, intelligence — what is called the candidate’s ‘image.’ My own conviction is that these images or impressions are likely to be uncannily correct.”

Kennedy and his appeal as a symbol of a new generation helped make TV “a substantive factor in American politics,” says Mary Ann Watson, who teaches at Eastern Michigan University and wrote a book on TV in the Kennedy years.

The president’s magnetic personality and his family’s knack for staging fairy-tale pictures attracted huge audiences. At the same time, the rivalry between NBC and CBS was heating up — ABC was not yet an equal competitor — and TV was just acquiring the technology needed to cover live events without extensive planning. In mid-1963, surveys asking Americans where they got their news put TV ahead of newspapers for the first time, a result of visual communal experiences such as the first space shots and early civil-rights demonstrations.

“You could read it in the paper, but, boy, seeing it was something else,” Watson says.

Never again would a president be without the “body watch,” the pool of correspondents and cameras that trail the chief executive’s every public movement.

Tom Wolfe, an essential chronicler of the ’60s, called the assassination “the prologue to America’s season of violence” — indeed, a new “pornoviolence,” in which images and narratives of death were incessantly repeated, hardening Americans against pain.

The TV networks, he wrote in 1967, “schooled us in the view from Oswald’s rifle and made it seem a normal pastime.” From then on, he argued, the center of the story, in news and entertainment programs, was not so much the hero but the aggressor, with gory details becoming the driving force of the narrative.

Actually, the four days of 24-hour television coverage that were most people’s experience of the assassination were remarkably free of explicit violence, but for the moment when Jack Ruby shot Oswald live on NBC. The dominant images were of mourning and an instant nostalgia — hours of clips of the Kennedy children at play, the bereft but stoic widow, the riderless horse moving through the streets of Washington, empty boots hanging backward in the stirrups.

Kennedy was frozen in youth and idealism, sanctified like no other president.

“The assassination coverage set in place the expectation that they really won’t show violence and they will bring us together,” says Barbie Zelizer, a professor at the University of Pennsylvania’s Annenberg School for Communication. “We learned that when something threatening happens, we go to our media for that collective experience that mitigates our pain.”

The news media would later stand accused of fomenting alienation, but that was several years off. Footage of the shooting would not air until more than 11 years later, when Geraldo Rivera showed bystander Abraham Zapruder’s film on an ABC show called “Good Night America.”

In the immediate aftermath, there was instead “a real sense of bonding with the newsman, a real sense of friendship that I don’t think people would feel now,” Bodroghkozy says.

Only after “the cynicism that came from Watergate, the violence of Vietnam, and the conspiracy culture of Hollywood in the ’70s” did a darker vision of America seem pervasive, she says. “By the time we get to the ’70s and two assassination attempts on Gerald Ford, they’re almost treated as a joke.”

In the cold midnight of the American century, images of a glamorous president and an optimistic young generation were suddenly confronted in the popular imagination by a lone gunman and whispers of conspiracy. The assassination became a symbol of all that seemed out of control — troubling images, brought home by television. Trauma coverage would become a finely honed routine, a ritual of spectacle that excites, unites, calms. A sameness of tragedy developed in which viewers could see carnage and mayhem as one stream of dark reality, whether war, natural disaster, terrorism or crime. The danger is that a generic and thin empathy becomes automatic, unthinking.

Some critics said the trauma of experiencing the assassination together helped bring about a troubling shift in the country’s personality; they called it an unraveling, a bursting of the bubble of American innocence. Art Bell, the late-night radio talk host whose show often focuses on conspiracy theories, called it the quickening, an acceleration of life in which Americans became more closely connected digitally yet ultimately more isolated, lonelier.

Oswald, the loner and searcher, killed a president and became a new, disturbing kind of media celebrity, what DeLillo in his novel “Libra,” called “a disaffected young man who suspects there are sacred emanations flowing through the media heavens and who feels the only way to enter this vortex is through some violent act of theater.”