Sixteen years after the U.S. Supreme Court outlawed racial segregation in public schools, an attorney representing black families in Charlotte stood before the court. The landmark Brown v. Board of Education ruling, he argued, had failed to deliver on its promise.

“Black children and parents in Charlotte have struggled since Brown,” said the attorney, Julius Chambers. He urged the high court to embrace a plan to integrate Charlotte schools through a controversial method: busing black children to white schools, and vice versa.

The Supreme Court agreed, unanimously endorsing busing as a legitimate means of unraveling the segregation of children by race. The 1971 decision launched an explosive chapter in American history, touching off a long and polarizing battle that set public opinion against busing for decades, even as the programs succeeded in promoting integration.

Later, evidence would emerge that busing improved outcomes for black students, with no harm to white students. But that evidence came far too late to change public perceptions of a program that was hugely unpopular among whites and left blacks divided.

The vexing issue has reverberated through the Democratic presidential primary since last month’s debates, when Sen. Kamala D. Harris (D-Calif.) criticized former vice president Joe Biden for opposing court-ordered busing in the 1970s. But Harris soon found herself backpedaling when asked whether she would advocate busing today: Last week, she called it a tool to be “considered” but mandated only if local governments are “actively opposing integration.”

That position is not so far from Biden’s, and not a single Democratic candidate is arguing for a return to mandatory busing. Sen. Bernie Sanders (I-Vt.) has promised to “execute and enforce desegregation orders” but has not said how. Most candidates have focused on creating incentives for districts and families to create diverse schools on their own.

“No one is really for compulsory busing today. Public opinion was never for compulsory busing,” said Richard Kahlenberg, senior fellow at the Century Foundation, a think tank that supports integration.

“Desegregation was highly successful. It provided a way to raise academic achievement for African Americans that was far more successful than anything we’ve tried since,” Kahlenberg said. “At the same time, it was a politically problematic way of achieving the goal.”

Even before the Supreme Court embraced busing in Swann v. Charlotte-Mecklenburg Board of Education, school desegregation was causing great agitation in American politics.

In 1954, the Supreme Court declared in Brown that schools that separated students by race were inherently unequal. In 1957, federal troops escorted nine black students into Little Rock’s Central High School. In 1960, 6-year-old Ruby Bridges needed the protection of federal marshals to enter kindergarten in New Orleans.

By the mid-1960s, it was growing difficult for most schools to ignore the issue. On the heels of the 1964 Civil Rights Act, which denied federal funding to any district that discriminated based on race, Congress approved a major education bill that contained significant funding for local districts.

Suddenly, Washington had powerful tools to pressure schools to desegregate. Under President Lyndon Johnson, the Department of Health, Education and Welfare, as it was known at the time, began wielding its new hammer.

Some communities acted voluntarily. In Berkeley, Calif., where Harris grew up, local officials implemented a full integration program in 1968 after a report showed that 14 of 17 elementary schools and two of three junior highs were segregated. Critics tried to recall the school board, but the vote failed, with 61 percent voting no.

Both black and white students boarded buses to new schools, among them Harris, who entered first grade in 1970.

But many communities dragged their feet, even after the Supreme Court spoke again in 1968. That year, Richard Nixon won the White House after pursuing a “Southern strategy,” stoking white resentment toward African Americans and promising to prevent “forced busing” of children. Opposition spread as the courts began ordering desegregation plans in cities outside the South, starting in Denver in 1973.

Amid the backlash, Biden, then a newly elected U.S. senator from Delaware, came out against busing. In a 1975 interview, one year before a federal court ordered busing in Wilmington, Delaware’s largest city, Biden called it “an asinine concept, the utility of which has never been proven to me.”

Biden was among the first liberal Democrats to side with conservatives and segregationists on the issue, and his support gave antibusing forces a burst of momentum in their effort to push back against the courts.

Talking to reporters last week, Harris said: “There were forces and individuals and supposed leaders in our country who actively worked against the integration of schools based on race. That is what was happening at that time. That’s why busing was mandatory at that time.”

Of Biden, she said, “He has yet to agree that his position on this, which was to work with segregationists to oppose busing, was wrong.”

In a speech Saturday in Sumter, S.C., Biden pushed back. Expressing regret for his recent remarks about working alongside segregationists in the Senate, Biden defended his opposition to busing and argued that segregated housing is the more pertinent target.

“The better answer is to get to the root cause of segregation,” Biden told a mostly African American audience. “I don’t believe a child should have to get on a bus to attend a good school. There should be first-rate schools of quality in every neighborhood in this nation.”

Polling from that time, and for many years to follow, shows that Biden was swimming in the mainstream. Surveys consistently showed majority support for the Brown decision against separate-but-equal education but widespread opposition to using busing to achieve racial integration.

A 1972 Harris Poll found that only 20 percent of Americans favored “busing schoolchildren to achieve racial balance,” with 73 percent against it. A 1978 Washington Post poll found that 25 percent agreed that “racial integration of the schools should be achieved even if it requires busing.”

African Americans were more supportive than whites but also had concerns. John C. Brittain, a civil rights attorney who litigated school segregation cases in that era, noted it was usually black schools that closed, black teachers who were fired and black children who were forced to travel.

“African Americans always had to bear the brunt of implementing school integration,” Brittain said.

In a 1973 Gallup poll, just 9 percent of black respondents chose busing as the best way to achieve school integration from a list of options. The most popular was creating more housing for low-
income people in middle-income neighborhoods.

Still, when asked directly by Gallup in 1981 whether they favored busing to achieve racial balance in schools, 60 percent of black respondents said yes, compared with 17 percent of whites.

Court-ordered busing was often met with protests. When busing began in South Boston in 1974, police patrolled in riot gear as hundreds of white demonstrators threw bricks and stones at buses arriving from the black neighborhood of Roxbury.

“The protests all fixate on this word ‘busing.’ Protesters never say they don’t want to go to school with black kids,” said Matthew F. Delmont, a history professor at Dartmouth College who has studied the history of busing. “They would say they are for desegregation but against busing.”

In many cities, white families fled to private schools or the suburbs, which often were not affected by busing orders. White flight reinforced the perception that busing was a mistake. Over time, the exodus of white families also made it harder for city school districts to create racially diverse schools.

Even as Boston erupted, Sen. Edward M. Kennedy (D-Mass.) spoke in favor of the program, emerging as one of busing’s most consistent champions. Some other Democrats were more cautious, if not opposed.

In 1972, Nixon’s Democratic opponent, Sen. George McGovern (S.D.), generally supported busing but sometimes downplayed the issue, at one point calling it “number 92” on his list of priorities. In 1976, Democrat Jimmy Carter campaigned against busing but then resumed civil rights enforcement efforts abandoned under Nixon. Historian Larry McAndrews called it a “calculated waffle.”

During these tumultuous years, Biden voted against some efforts to curb busing, taking heat from some constituents. But he also tried repeatedly to curb the power of the federal government and the courts, and he criticized the explicit racial quotas that busing was often employed to deliver.

“The new integration plans being offered are really just quota systems to assure a certain number of blacks, Chicanos, or whatever in each school,” he said in 1975. “That, to me, is the most racist concept you can come up with.”

In 1980, Republican Ronald Reagan was elected as president after opposing busing on the campaign trail. Civil rights leaders were offended, insisting: “It’s not the bus, it’s us.”

Yet busing was working in some places, notably Charlotte.

After initial opposition and some violence, “an amazing thing started happening: People said we can’t keep doing this. We’re going to lose our school system if we don’t find some way to make this work,” said Frye Gaillard, who covered that period for the Charlotte Observer and later wrote a book about it.

Under the original plan, children in central Charlotte typically were forced to travel farther than children on the district’s suburban fringes. Urban parents — working-class blacks and whites — demanded a more equitable arrangement. It worked, Gaillard said. City leaders supported a new approach, and the resulting program became a point of civic pride.

“It was really a dramatic story to see it unfold,” said Gaillard, whose three children were bused. “A city diving into the implications of its segregated past, going through all sorts of turmoil and ugliness for a few years and then coming out the other side. There was this perverse Southern pride: ‘We can do it, and they can’t do it in Boston.’ ”

When Reagan denounced busing as “a social experiment that nobody wants” during a campaign stop in Charlotte in 1984, the crowd, once rapturous, responded with stony silence, according to Gaillard and news reports at the time.

Experts say school desegregation reached its pinnacle in 1988. After that, Nixon and Reagan appointees shifted the Supreme Court to the right, and the court declared that districts could escape desegregation orders if they proved their districts had eliminated the vestiges of past discrimination.

One by one, the plans were undone. And in 2007, the high court invalidated the use of race as a criterion in assigning students to schools.

Today, fewer than 200 desegregation plans remain in force, down from more than 1,000, according to an estimate by Erica Frankenberg, an expert on school segregation at Pennsylvania State University. Rather than mandatory busing, integration activists now call for voluntary initiatives, such as magnet programs to attract white students to schools in nonwhite neighborhoods.

And opposition to busing appears to remain strong. A 2004 Associated Press-Ipsos poll, one of the few to ask about busing in recent years, found that 78 percent of Americans surveyed preferred letting students go to their local school even if it meant most people would be of the same race. Only 19 percent said it would be better to transfer students to other schools to create more integration.

While segregation has increased in many places, it remains lower than before busing. And that may be reason enough for Democrats like Biden to acknowledge that busing had value in its day, said Leon Panetta, the former Pentagon and CIA chief who, as a young man in the late 1960s, led the federal education office pushing schools to integrate.

“Frankly, Joe would be better off to say [his opposition to busing] was a mistake and kind of move on. Because, frankly, it was important to the effort to provide equal education,” Panetta said in an interview.

“In the end, what everybody has to understand is, if we were going to implement Brown v. the Board of Education and do it effectively, it was necessary to consider busing,” Panetta said. “That was the only way to get these kids to school.”