At the beginning of 1968, no one could have predicted the reception that would greet President Lyndon Baines Johnson as he entered St. Patrick's Cathedral in Manhattan on the afternoon of Thursday, April 4. Here was a man so dogged by protesters that he had been limiting his public appearances to military bases and American Legion halls. Here was an activist president—his legislative achievements were exceeded only by those of his idol, Franklin D. Roosevelt—who had become so divisive that he had abandoned his re-election campaign just four days before. And yet, as he began walking down the aisle with his daughter Luci, the 5,000 people who had gathered for the installation of Terence Cooke as archbishop of New York rose and began to applaud. As the president and his daughter sat silently through Cooke's inaugural sermon, the archbishop addressed him directly: "Mr. President, our hearts, our hopes, our continued prayers go with you."

The greeting in New York City was just the latest manifestation of a dramatic turn in Johnson's popularity. Hundreds had lined the streets to see his motorcade as it entered the city. Another crowd had cheered him during a visit to Chicago three days earlier. Newspaper editorials had heaped praise on Johnson for his decision not to seek re-election. It was as if someone had flipped a switch in the national psyche: in a Harris Poll taken after his withdrawal announcement the previous Sunday night, the public went from 57 percent against to 57 percent in favor of the job he was doing as president.

After dropping his campaign, Johnson was by all accounts a man renewed. An increasingly hostile Congress, constant public criticism, the recent Tet Offensive by Viet Cong and North Vietnamese forces, and the prospects of a grueling re-election battle had ground him to a nub; now, freed from political pressures and embraced by the media and public, he plotted an agenda for his remaining months. Along with peace in Vietnam, he had a long list of domestic programs he felt he now had the political capital to get passed. As he wrote in his memoirs about his New York visit, "The world that day seemed to me a pretty good place."

But then, just hours after Johnson entered St. Patrick's, James Earl Ray poked his Remington Gamemaster out the bathroom window of a Memphis flophouse and fired at the Rev. Dr. Martin Luther King Jr., who was standing outside his room at the Lorraine Motel, 80 yards away. King was rushed to a nearby hospital, where he died at 7:05 p.m.

An aide relayed the news of the shooting to Johnson as he sat meeting with Robert Woodruff, head of Coca-Cola, and former Georgia governor Carl Sanders in the West Wing of the White House; word of King's death came within an hour. The president finished his business quickly, then huddled with his inner circle of aides to work on a statement he would read on television. Before the night was out, looting and burning erupted in Washington, just blocks from the White House; over the next several days, riots would break out in as many as 125 cities. When it was over, 39 people were dead, more than 2,600 injured and 21,000 arrested; the damages were estimated at $65 million—the equivalent of about $385 million today—though the destruction was so widespread that a full accounting remains impossible.

Back in the White House, even as the riots were beginning, Johnson knew his hopes for a legislative victory lap were finished. Just hours after King's death, he told his domestic policy adviser, Joseph A. Califano Jr.: "Everything we've gained in the last few days we're going to lose tonight."

Johnson had weathered riots before—the first of the "long, hot summers" was in 1964, only months into his presidency. But by 1968 he knew that another spasm of urban disorder would ruin his standing with the public. Far more than Vietnam, a combination of civil rights activism and racial riots had eroded LBJ's support among white, middle-class Americans. "The level of vitriol in the mail and the calls over all the race issues dwarfed anything we had on Vietnam," Califano told me recently in the Manhattan office where he chairs the National Center on Addiction and Substance Abuse. "He was very conscious that he'd become an incredibly divisive figure because of his strong stand on the race issue."

Nevertheless, Johnson began 1968 hoping he could push through his ambitious domestic agenda while running for re-election: among other items, a 10 percent income tax surcharge, a ban on housing discrimination and more money for the Head Start school-readiness program, housing and jobs. "In January he was still willing to spend whatever capital he had left—and it was dwindling fast—to get his work done without waiting for the war to be over," Califano wrote in his memoirs. "Often we put so many complex proposals out in a day that reporters were unable to write clearly about them." But the disastrous Tet Offensive in January and February and antiwar Senator Eugene McCarthy's striking second-place finish in the New Hampshire primary in March convinced Johnson that he had to do something drastic. "Abdication," historian Doris Kearns Goodwin wrote in her biography of Johnson, "was thus the last remaining way to restore control, to turn rout into dignity, collapse into order."

Conventional wisdom holds that Johnson backed out of the 1968 race a broken man, undone by years of domestic division. But 40 years later, such a view seems too simplistic. An examination of that fateful week in the Johnson presidency, based on documents from the National Archives and interviews with Johnson White House staffers, shows that he was, in fact, emboldened by his withdrawal—only to be broken, finally and irreparably, by the King assassination and the riots that followed.

Indeed, soon after he made his withdrawal address, Johnson was plotting a new agenda. "His demeanor was that of a new man," his confidant and former speechwriter Horace Busby wrote. "His conversation began to quicken with talk of what could be achieved over the balance of the year. There was fresh excitement and an old bite in his tone as he declared, ‘We're going to get this show on the road again.'"

But the show closed quickly. Consider the fate of a speech, conceived in the hours after King's death, to outline a massive new effort to address urban poverty. On Friday, April 5, the day after King died, Johnson had gone on television and promised to deliver the speech the following Monday. Then he pushed it back to Tuesday night, supposedly to avoid overshadowing King's funeral in Atlanta earlier that day. Then he postponed it indefinitely. When Busby urged him to get on with it, Johnson demurred. "We don't have the ideas we used to have when I first came to this town," he told Busby. "Until we all get to be a whole lot smarter, I guess the country will just have to go with what it has already."

Johnson's withdrawal—which he announced on March 31 on national television with the words "I shall not seek, and I will not accept, the nomination of my party for another term as your President"—was long in coming. According to his press secretary George Christian, Johnson had been weighing the decision since October, and he had casually broached the subject with friends even earlier. In January 1968, he asked Busby to draft a withdrawal statement to slip into his State of the Union address, but the president never delivered it.

By late March, however, Johnson had begun to reconsider. At lunch on Thursday, March 28, he brought up the idea of withdrawing with Califano and Harry McPherson, his special counsel. With antiwar protesters outside the White House gates chanting, "Hey, hey, LBJ! How many kids did you kill today?" Johnson rattled off his reasons for withdrawing. He was worried about his health. He wanted to spend time with his family. Most important, his political capital was gone. "I've asked Congress for too much for too long, and they're tired of me," he told his lunch companions, according to McPherson, now a partner at a Washington law firm.

Johnson's staff had spent weeks working on a major speech about Vietnam, scheduled for the evening of March 31, in which the president would announce a halt to bombing over most of North Vietnam to encourage Hanoi to enter peace talks. The day before, he asked Busby to rework the statement that had gone unread during the State of the Union address. Busby came to the White House the next morning, and Johnson secluded him in the Treaty Room to work on what Johnson discreetly called his "peroration."

Johnson told his vice president, Hubert Humphrey, about the new ending that morning, but informed key cabinet members only minutes before going on the air. As he sat in the Oval Office, his family watching from behind the cameras, he exuded a calm rarely seen on his face of late, "a marvelous sort of repose over-all," recalled his wife, Lady Bird. When he finished his speech, he stood quietly and hugged his daughters.

The White House was silent. "We were stunned," McPherson told me. And then the phones began ringing. All night, friends close and estranged called with congratulations and approval. The White House press corps exploded in activity, clamoring for a further statement. The first lady finally emerged. "We have done a lot," she told reporters. "There's a lot left to do in the remaining months; maybe this is the only way to get it done."

Johnson addressed the nation on television again the night of April 4. "America is shocked and saddened by the brutal slaying tonight of Dr. Martin Luther King," he said. "I ask every citizen to reject the blind violence that has struck Dr. King, who lived by nonviolence."

He had already called King's widow, Coretta; now, he dived into a flurry of calls to civil rights leaders, mayors and governors around the country. He told the civil rights leaders to go out into the streets, to meet with people and express their sorrow. He advised politicians to warn their police against the unwarranted use of force. But no one seemed to be heeding his words. "I'm not getting through," he told his aides. "They're all holing up like generals in a dugout getting ready to watch a war."

Busby, who had come in from his Maryland home to help with any speechwriting, watched as his old friend once again took on the weight of a national emergency. "The exuberance of the week seemed to be draining from his long face as I watched him behind the desk," he later wrote.

Johnson dispatched a Justice Department team, led by Attorney General Ramsey Clark, to Memphis to oversee the manhunt for King's assassin. Meanwhile, he set Califano, McPherson and their assistants to work calling the nation's leading black figures to a meeting at the White House the next day: Roy Wilkins of the NAACP; Whitney M. Young Jr. of the National Urban League; Mayor Richard Hatcher of Gary, Indiana; Thurgood Marshall of the U.S. Supreme Court; and around a dozen others. Martin Luther King Sr. was too ill to come from his home in Atlanta. "The president wants you to know his prayers are with you," one of Johnson's aides told him over the phone. "Oh no," replied the ailing patriarch, "my prayers are with the president."

In Washington, the night was warm and cloudy, with rain in the forecast. As news of King's death spread, crowds gathered on U Street, the center of the city's downtown black community about 20 blocks north of the White House, to share their shock, grief and anger. At 9:30, someone broke the plate-glass window at a Peoples Drug Store; within an hour, the crowd had turned into a mob, breaking shop windows and looting. A light rain before midnight did little to disperse the crowd. Soon rioters set several shops ablaze.

Volleys of police tear gas brought the rioting under control by 3 a.m. Friday; by dawn, street-cleaning crews were sweeping up broken glass. And though scattered looting and violence had erupted in more than a dozen other cities, it seemed that the country had emerged from the night remarkably intact. The question was whether rioting would resume that night.

Friday, then, was a day for grieving and waiting. The House of Representatives observed a moment of silence. The Senate heard eulogies for an hour, after which House and Senate liberals called for immediate passage of fair-housing legislation, which had been stymied for almost two years. In Atlanta, preparations began for King's funeral the following Tuesday. But by and large, the country tried to adhere to routine. Most schools opened, as did federal and private offices in Washington.

At the White House, Johnson and the assembled black leaders gathered in the Cabinet Room, along with Democratic Congressional leaders, several cabinet members and Vice President Hubert Humphrey. "If I were a kid in Harlem," Johnson told them, "I know what I'd be thinking right now: I'd be thinking that the whites have declared open season on my people, and they're going to pick us off one by one unless I get a gun and pick them off first."

That can't be allowed to happen, he continued. That's why he had called the meeting. Resoundingly, his guests told him that words weren't enough; with King gone, black citizens needed to see action in order to believe that there was still hope for progress. Otherwise, the country could experience untold violence in the coming days.

Johnson promised immediate, concrete action. Then, accompanied by the leaders, he went by 12-car motorcade to a memorial service at Washington National Cathedral, where King had addressed an overflow crowd just five days before. "Forgive us for our individual and our corporate sins that have led us inevitably to this tragedy," intoned King's Washington representative, the Rev. Walter Fauntroy. "Forgive us, forgive us. God, please forgive us."

Upon returning to the White House, Johnson read another statement on television promising to address Congress that Monday with a list of new social spending plans. "We must move with urgency, with resolve, and with new energy in the Congress, in the courts, in the White House, the statehouses and the city halls of the nation, wherever there is leadership—political leadership, leadership in the churches, in the homes, in the schools, in the institutions of higher learning—until we do overcome," he said.

Afterward, Johnson sat down to lunch with Luci, Busby, McPherson, Califano and Supreme Court Justice (and longtime adviser) Abe Fortas. Before they began eating, Johnson bowed his head and said, "Help us, Lord, to know what to do now." Looking up, he added, "I thought I'd better get specific about it, fellas." Halfway through the meal, one of the men got up and went to the window overlooking Pennsylvania Avenue. "Gentlemen, I think you'd better see this," he said. Through the budding trees they spied a flood of cars and people, all pushing their way westward out of the city.

Johnson and others moved from the dining room to the sitting room. The president looked down the long hall of the White House toward the east and pointed silently. Out the window, past the Treasury Building, a column of smoke was rising from downtown Washington.

By 1968, the White House was well-versed in crisis management. As reports of rioting across the city began streaming in, Johnson called in Cyrus Vance, the former deputy secretary of defense who had overseen federal efforts during the 1967 riots in Detroit, from his law office in New York to help coordinate the Washington response. D.C. Mayor Walter Washington set a curfew of 5:30 p.m. Califano established a White House command center in his office, while the city government set one up at the mayor's office. At one point, Califano handed the president a report saying that militant African-American leader Stokely Carmichael was planning a march on Georgetown, home to many of the media elite LBJ so disdained. "Goddamn!" the president caustically joked. "I've waited thirty-five years for this day."

By 5 p.m. federal troops occupied the Capitol, surrounded the White House and had begun patrolling with sheathed bayonets; ultimately, some 12,500 soldiers and National Guardsmen would be sent to Washington. Tanks crunched broken glass beneath their treads. And Washington wasn't the only city to be occupied. "At about five o'clock in the afternoon, Johnson got a call from Mayor [Richard J.] Daley, who started telling him Chicago was getting out of control," McPherson told me. Federal troops soon arrived in Chicago. They marched into Baltimore on Sunday.

Scores of cities across the nation registered some level of civil disturbance. Pittsburgh and, later, Kansas City, Missouri, teetered on the edge of uncontrollable violence. In Nashville, rioters torched an ROTC building. National Guard troops were deployed in Raleigh and Greensboro, North Carolina. Even small, previously peaceful cities were hit—in Joliet, outside Chicago, rioters burned down a warehouse not far from a key Army munitions factory.

Flying home from Memphis on Friday evening, Attorney General Clark and his staff had asked the pilot to circle Washington before landing at Andrews Air Force Base. Roger Wilkins, then an assistant attorney general, recalled seeing fires everywhere, obscured by billowing smoke. "As I'm looking out the window, I see a great big orange ball with a needle in it," he told me. "All of a sudden I said...‘That's flames, and the needle I'm seeing is the Washington Monument.' The city looked like it had been bombed from the air."

Along with the riot response, Johnson's aides went to work on the speech the president was scheduled to give to Congress that Monday. The address, Johnson told Busby, "can make or break us. The [withdrawal] speech Sunday was good and accomplished what we wanted, but King's death has erased all of that, and we have to start again."

Proposals poured in: LBJ's Congressional liaison, Harold "Barefoot" Sanders, suggested a bigger income surtax. The Labor Department suggested a renewed effort to rehabilitate ghettos. Gardner Ackley, chairman of the Council of Economic Advisers, suggested a "bill of economic rights" that would give priority to programs for housing and income assistance. Doris Kearns Goodwin, then a White House fellow assigned to Labor, recalled working late into the night on the speech, then "driving home exhausted through uncanny, deserted streets, halted periodically at barricades where armed soldiers looked inside the car." At one point, Califano's staff tallied $5 billion (the equivalent of almost $30 billion today) in new plans to include in the speech. "One thing people were of a single mind about," McPherson told me, "was that it shouldn't be any small measures."

But as Friday gave way to Saturday and then Sunday, the mood in the White House soured. The speech was repeatedly postponed. By April 9, the Washington Post noted, "Neither Congress nor the Administration appeared in a mood to plunge headlong into massive new urban spending programs now."

What had happened? In part it was simple realism. Even as Johnson was drumming up his list of new programs—an expression of his unalloyed New Dealer faith in government—he was hearing new levels of criticism and anger from his friends in Congress. Georgia Senator Richard Russell, one of Johnson's fellow Democrats, phoned and fumed because he had heard that the soldiers guarding the Capitol were bearing unloaded arms. (They did, however, carry ammunition on their belts.) West Virginia Senator Robert Byrd, another Democrat, called for the Army to occupy Washington indefinitely.

It was "extraordinary that there should have been such a vast difference between the conversations in the White House and attitudes on the Hill," McPherson wrote in his memoirs. "On the Hill, and probably for the majority in this country, [new social spending] seemed dangerously like a protection racket."

On Sunday, Johnson saw the destruction in Washington firsthand. After attending church with Luci, he accompanied Gen. William Westmoreland—who had flown in from Vietnam for a meeting—on a helicopter trip to Andrews Air Force Base. On the way back, he had the pilot fly up and down the riot-torn streets. In the daylight, recalled Tom Johnson, a White House aide (and future president of CNN), the passengers could still see fires burning.

With America in flames, Johnson realized that he would do better to focus his efforts on a single piece of legislation, preferably one with few costs attached. He chose the fair- housing bill, which would ban racial discrimination in housing sales and rentals for some 80 percent of the residential market. It was, noted Senator Sam Ervin, a Democrat from North Carolina, the first civil rights bill to challenge discrimination outside the South. For that reason—combined with the national cooling on civil rights since the 1965 Watts riot—it had been stalled for two years.

But King's assassination gave the bill new life. The Senate had already passed it; the House followed suit on Wednesday, April 10. Johnson signed the bill the next day, a week after King's death, surrounded by 300 friends, staffers, civil rights leaders and members of Congress. Taking note of the violence of the past few days, he said, "The only real road to progress for a free people is through the process of law." He also pleaded with Congress to pass legislation he had already introduced for social programs totaling $78 billion ($465 billion today). "We have come some of the way, not nearly all of it," he said.

But by then his power was spent. He would get his surtax passed later that year, but only after agreeing to painful spending cuts. Congress would approve a plan for new low-income housing, but it was a GOP-backed plan. Johnson couldn't even claim full credit for passage of the fair-housing bill: Richard Nixon, who was pursuing the Republican nomination for president, telephoned GOP legislators that weekend urging them to support it, the better to remove civil rights from the coming campaign. The bill also included a ban on transporting or teaching the use of firearms and incendiary devices deployed in riots, making it palatable to law-and-order advocates. And in the end, Congress refused to provide money to enforce the ban on discrimination.

Johnson may be remembered as the Vietnam War president, but in his mind his greatest legacy was his efforts to improve the lives of African-Americans. And he had much to show for it: the 1964 Civil Rights Act, the Voting Rights Act, the War on Poverty, Head Start and more. But as the 1960s wore on, he also saw himself in a race—against black militancy, against rising ghetto frustrations, against an increasingly conservative white electorate.

At times, he privately lashed out at black America. "I asked so little in return," he later lamented to Kearns Goodwin. "Just a little thanks. Just a little appreciation. That's all. But look what I got instead....Looting. Burning. Shooting. It ruined everything." And April 1968 was the final blow. In a telling memo from April 10, Califano confronted his boss: "You are publicly on record promising a message. Failure to deliver will be considered a breach of faith by the entire Negro community and a good deal of the influential white community." Johnson scribbled angrily in reply, "I promised nothing. I stated my intentions only. Since changed by riots."

More than wounding his pride, the riots forced Johnson to realize how little his efforts had actually changed the country, at least in the short term. He had naively hoped that a massive assault of federal spending would relieve conditions in the ghetto overnight; when 125 cities erupted over one weekend, he had to confront the fact that nothing he had done seemed to have had an effect. "God knows how little we've really moved on this issue, despite all the fanfare," he later told Kearns Goodwin. "As I see it, I've moved the Negro from D+ to C-. He's still nowhere. He knows it. And that's why he's out in the streets.

"Hell," he added, "I'd be there too."

Clay Risen is the author of A Nation in Flames: America in the Wake of the King Assassination, due out in spring 2009.