On March 31, 1968, Lyndon B. Johnson appeared on national television and announced that he was partially halting the U.S. bombing of Vietnam, and that he had decided not to seek his party’s nomination for president. “There is division in the American house now,” Johnson declared.

The news that the President had refused to seek re-election sent waves of shock and elation through a stunned electorate. At the same time, his withdrawal from the race crystallized the nature of the conflicts that had split the country along ideological, racial, and class lines so deeply. But within days it became all too apparent that no single act of political sacrifice could repair the divisions in the country. Johnson’s presidency was a symbol and a reflection of the nation’s fissures, but it was not ultimately its root cause.

Johnson himself alluded to the deep roots of the unraveling of America in his surprise announcement: “With America’s sons in the fields far away, with America’s future under challenge right here at home, with our hopes and the world’s hopes for peace in the balance every day,” he said, “I do not believe that I should devote an hour or a day of my time to any personal partisan causes or to any duties other than the awesome duties of this office—the Presidency of your country.”

His refusal to run again was, on some basic level, a recognition of political reality. For all his legislative achievements (the Civil Rights Act of 1964, the Voting Rights Act of 1965, Medicare and Medicaid), LBJ had become the face of America’s divisions. To those on the Right, Johnson had done too much, too quickly, overloading the system with big-government programs that trampled on individual liberties. Much of the Left viewed Johnson as the corrupt wheeler-dealer who had lied America into the disastrous, bloody Vietnam quagmire.

LBJ faced long odds in November; his top aides feared that he might not even win re-nomination. With his public approval rating at around 36 percent, LBJ had barely survived a surprisingly strong primary challenge from antiwar Sen. Eugene McCarthy in New Hampshire, who took 42 percent of the vote to LBJ’s 48 percent on March 12. Four days later, on March 16, New York Sen. Robert F. Kennedy, a long-time LBJ nemesis, declared that he, too, would challenge Johnson for the nomination.

Presidents rarely refused to stand for a full second term. But Johnson’s handling of the war in Vietnam hung albatross-like around his White House. He had repeatedly lied about America’s military progress, and the Tet Offensive in which Viet Cong troops attacked key cities in South Vietnam in January disproved the administration’s confidence that victory was just around the corner. (Harry Truman, similarly saddled with the unpopular Korean War, refused to run in 1952.)

Johnson’s leading Republican contender Richard Nixon may well have trounced Johnson in November had he stood for a second term. As Johnson’s withdrawal caused turmoil within the Democratic Party, Republicans appeared to have the upper-hand in the race to retake the White House.

LBJ’s announcement was so dramatic partly because it was so unexpected. When LBJ sat down to deliver the speech, even he wasn’t certain that he would utter the words his aides had written for him. LBJ had acquired a reputation, rooted in decades of service in Senate leadership and then in the White House, as a brilliant legislative operator, a masterful manipulator of men and laws, a politician who wished both to advance his own self-interest and outdo FDR as the greatest reform president of the 20th century.

By March 1968, however, “Landslide Lyndon,” so named after his 1948 senate primary win against Coke Stevenson, had become gripped with anxiety, insecurity, and uncertainty over the war, inner-city riots, and the perceived failure of the war on poverty.

The two serious Democratic primary challengers already in the race, McCarthy and Kennedy, along with their aides and allies reacted to Johnson’s surprise announcement to not run against them with a combination of effusive glee and unsettled confusion about what his departure would mean for their chances of winning the presidency. Upon hearing Johnson’s announcement, RFK’s friend Jim Whittaker placed a call to Kennedy and told him, “Congratulations,” as if the candidate had just won the nomination.

McCarthy gave credit for Johnson’s withdrawal from the race to antiwar activists in general and those who had volunteered on his campaign in particular. Referring to Johnson’s supporters, McCarthy said, “I don’t think they could stand up against five million college kids just shouting for peace. There was too much will-power there.”

Richard Goodwin, a former LBJ speechwriter who had joined McCarthy’s campaign in protest of the Vietnam War, felt “stunned, then exultant” when he heard Johnson say he would leave the White House in January. Goodwin leapt out of his chair, approached the television set, and pointed at Johnson. “I thought it would take another six weeks,” he said.

But Johnson’s withdrawal also raised some hard questions for Democrats. The candidates and their allies feared that Johnson’s decision might sap the energy that had provided them with much political attention and excitement from the moment they announced their primary challenges. As Democratic leaders struggled to figure out how to respond to Johnson’s sudden withdrawal, antiwar activists rejoiced.

Their movement, some of them concluded, had forced Johnson to alter his war policy and to decide that he could not win another term. From Madison, Wisconsin, to Berkeley, California, students honked their horns and held spontaneous street parties as a rare burst of jubilation took hold. Perhaps the war would finally begin to end now that Johnson was bowing out of the race.

At the same time, the decision provided a short-term jolt to Johnson’s political standing. Much of the public and the news media interpreted Johnson’s announcement as a Godsend that made the project of national repair more feasible for 1968; LBJ’s withdrawal offered hope, however scant, of national reconciliation, hope that new leaders would step up and somehow unite a fractured Republic. Johnson’s decision not to seek re-election was a sign that the political system was still responsive to the people’s will.

In this spirit, newspaper editorials praised Johnson’s decision as a strong step toward healing, and a Harris poll revealed that Johnson’s numbers had climbed from 57 percent disapproval of his job performance to 57 percent approval as a result of his decision not to run again.

Yet the impression that this was a moment of national reunification engendered by Johnson’s withdrawal was merely a chimera. It shimmered on the surface of national politics and it was a mirage in the final analysis. In bowing out of the race, Johnson had merely papered over divisions that had been in the making for years, or even decades. Most shattering of all, the pace and scale of events undercut any lasting momentum toward unity gained through Johnson’s announcement.

Five days after the speech, James Earl Ray, a small-time criminal with racist views, shot and killed Martin Luther King Jr. as he was standing on the second-floor balcony of the Lorraine Motel in Memphis, Tennessee.

“Everything we’ve gained in the last few days we’re going to lose tonight,” Johnson predicted to his aide Joseph Califano. Riots soon tore through more than 100 American cities.

Just two months later, in June of 1968, 22-year-old Sirhan Sirhan shot and killed Robert F. Kennedy at the Ambassador Hotel shortly after Kennedy’s victory in the California primary. His assassination deprived Democrats of their best antiwar candidate with some ability to bring together African-Americans and the white working-class in a year when segregationist Alabama Gov. George Wallace’s third-party candidacy was surging.

Johnson’s decision was not all it was cracked up to be. He remained the de facto leader of the Democratic Party and he continued to be the Party’s Kingmaker, insisting that his handpicked successor, Vice President Hubert Humphrey, endorse the administration’s war policies and stay loyal to Johnson. Humphrey had enough support among delegates to win the nomination at the party’s violent, fractious convention in Chicago that summer, and the party’s platform by and large reflected Johnson’s views of the war and endorsed his continued military commitment to Vietnam.

Johnson’s withdrawal from the race also gave conservative Republicans a long-awaited opening. Johnson’s partial bombing halt and his pledge to seek a negotiated peace in Vietnam gave leading Republican presidential candidate Richard Nixon space on the Vietnam question. Rather than having to specify his plans for ending the war in Vietnam honorably, Nixon was now able to fudge the details and instead say he wanted to give Johnson’s proposals a chance to be successful.

As we now know, the United States would go on to lose tens of thousands of lives in Vietnam before its final withdrawal from the country in 1975. In the long run, Republicans were able to use the end of Johnson’s career as a coda for what they charged was the ruin liberalism had brought both to the domestic United States and the arenas of foreign and military policy. Conservatives asserted that Johnson had micromanaged and lost the war in Vietnam by refusing to unleash the full military arsenal of the United States.

They further claimed that LBJ’s Great Society had ushered in a period of heightened racial tensions, worsened the plight of the urban poor, and raided the white workingman’s pocketbook to pay for programs aimed at helping the poor and racial minorities. Thus Johnson’s exit from the race became a pivotal symbol in the rise of modern conservatism, confirming for conservatives that a titanic liberal such as Johnson had to end his presidency in disgrace because liberalism had yielded a series of miserable failures. Republicans saw the speech as proof that Johnson—and his agenda—were unworkable and had been defeated.

With his policies under fire from all directions, and his popularity at a nadir, the most powerful man in America was forced into early retirement. Richard Nixon ultimately defeated Hubert Humphrey in November, of course, although it’s conceivable that he would have won an even more commanding victory had the unpopular Johnson stayed in the race.