The second round of the first Democratic primary debates on June 27 included a revealing — and at times tense — discussion of race between several candidates. A defining moment was when Sen. Kamala Harris took former Vice President Joe Biden to task over his recent comments about segregationist senators, as well as his opposition to using federally mandated busing to racially integrate schools in the 1970s. She pointed directly to how busing affected her life as a young child.

“You also worked with [those segregationist senators] to oppose busing,” Harris said, speaking directly to Biden. “And there was a little girl in California who was part of the second class to integrate her public schools and she was bused to school every day. And that little girl was me.”

“I did not oppose busing in America,” Biden, who represented Delaware in the US Senate from 1973 to 2009, responded. “What I opposed is busing ordered by the Department of Education. That’s what I opposed.”

There was a little girl in California who was bussed to school. That little girl was me. #DemDebate pic.twitter.com/XKm2xP1MDH — Kamala Harris (@KamalaHarris) June 28, 2019

In raising busing specifically, Harris hit on a part of Biden’s record that the former vice president hasn’t really discussed publicly in recent years: his support of legislation that aimed to limit the federal government’s ability to enforce court-ordered busing mandates, at the time the fastest-acting tool to promote school desegregation. As Vox’s Ella Nilsen reported, the Biden campaign swiftly moved to push back on Harris’s argument, issuing a statement that Biden’s busing stance had been misrepresented at the debate.

“When Biden said it wasn’t true that he supported anything that would have stopped the busing program that impacted her, he was correct,” the Biden campaign said. “None of [Biden’s] votes would have negatively impacted the Berkeley School Busing Program.” (Berkeley began its voluntary busing program in 1968, five years before Biden entered the Senate.)

Since the debates, Harris, as well as Sen. Cory Booker, has continued to press Biden on the issue, saying that his stance at the time was troubling given how many states had to be forced into following civil rights rulings and legislation. “I literally leaned back in my couch and couldn’t believe that one moment,” Booker, who participated in the debates on Wednesday, said of Biden and Harris’s exchange during a June 28 CNN interview.

“I think that anybody that knows our painful history knows that on voting rights, on civil rights, on the protections from hate crimes, African Americans and many other groups in this country have had to turn to the federal government to intervene because there were states that were violating those rights,” he added.

In an election cycle where Democratic candidates have issued a flurry of policy proposals that are far more progressive than previously seen, these critiques of Biden are clearly intended to make a broader point: that the former vice president, in continuing to defend—or at least not apologize for—his stance on busing, is out of step with the current Democratic electorate on issues of race and fighting racism. And that could be an issue for many of the black voters Biden is counting on for support.

In reality, though, things are more complicated. Busing has historically been unpopular among many white Americans and has also been criticized in some black communities. In more recent polling, there’s been little indication that white attitudes about busing have changed all that much from when Biden was a young US senator. Opposition to actions that would forcefully desegregate America’s increasingly segregated schools remains high in places like New York City, for example, where some white parents have opposed some proposals to diversify schools.

It suggests that Biden’s view — that desegregation is an important goal, but the federal government should only intervene in cases of segregation deliberately created by policy — might not be a problem for many voters.

Harris’s own stance on the issue has also muddied the waters. While she launched a powerful attack on Biden’s record at the debate, she’s stopped short of calling for busing herself. Her position has caused the Biden campaign to argue that Harris’s stance isn’t all that different from what she criticized Biden for.

In the weeks since the debate, Biden apologized for his earlier comments praising segregationists. But he has maintained that he was not wrong to oppose busing in the 1970s, pointing to his Senate votes on things like the Voting Rights Act and his tenure as vice president as indications of his strong support of civil rights.

As of now, it’s unclear if Biden will suffer any lasting damage in the polls. Even so, this part of Biden’s record — and his efforts to move past it — have raised questions about the former vice president’s ability to address racial justice issues in the present. And a closer look at his record shows that his opposition to busing was far more extensive than he has acknowledged.

America’s history of busing, explained

When the Supreme Court’s 1954 ruling in Brown v. Board of Education found school segregation unconstitutional, schools were expected to begin the process of desegregating. The Brown ruling and the Supreme Court’s 1955 ruling in a follow-up case known as Brown II determined that it was up to the states to figure out how they would integrate.

Many states responded by simply doing nothing, refusing integration outright (some went so far as to close their school systems entirely rather than integrate). That inaction and resistance, coupled with already existing residential segregation (much of it directly caused by policy), meant that schools remained heavily segregated a decade after Brown. Frustrated by this, civil rights activists turned to the courts and the federal government for an intervention.

These court-mandated desegregation interventions took the form of what was later referred to as “busing”— a process where black students were driven to predominantly white schools in neighboring communities, and white students were driven to predominantly black ones (however, not every busing program was a two-way program — many only had black students bused to predominantly white schools).

According to Matthew Delmont, a historian at Dartmouth and author of Why Busing Failed: Race, Media, and the National Resistance to School Desegregation, the history of busing itself actually goes back further, to when school buses were used to maintain segregation. Prior to the 1960s, school districts often bused white students to all-white schools, while black students were sent to predominantly black schools, even if doing so meant transferring students across district lines.

“It’s only when busing gets linked to school desegregation that it becomes an issue,” Delmont explained in an interview with Vox. Busing “becomes a political codeword and a way for white parents to say ‘we oppose this change’ without saying that they oppose their children going to schools with black and Latino students.”

One of the earliest instances of black and Latino students being bused to predominantly white schools was in the 1950s, Delmont said. New York tried to reduce overcrowding in predominantly black schools by sending a small amount of students to white schools. Those efforts quickly led to protests from white parents.

However, it wasn’t until the late 1960s and early 1970s that busing became more frequently used to promote school integration. There was no single way for busing to be implemented in a community, and some school districts, like Berkeley, decided to adopt busing programs voluntarily after outcry from activists. But many busing orders were mandated by courts after civil rights groups like the NAACP filed — and later won — school desegregation lawsuits.

Busing was often used as a last resort for cities and districts that clearly showed little interest in desegregation, many of which continued to see black and white families live in different communities and attend different schools. It was used to immediately desegregate schools in the hopes of not only ending state-sanctioned segregation of blacks and whites, but to also give black and white students equal access to resources and opportunities. Many of these opportunities had been isolated to white schools in white communities. Predominantly black and Latino schools, meanwhile, struggled with overcrowding, outdated materials, and dilapidated buildings.

Despite the goals of busing — which was intended to be just one of several tools used to secure black students’ constitutional right to equal education — the practice was often strongly opposed by white parents, many of whom did not want their children in integrated schools. Some parents and lawmakers stated that outright, but others used different anti-busing arguments: that their children were being placed in lower-quality schools (ignoring that schools in predominantly black neighborhoods had fewer resources and that per pupil spending on black students was smaller), or that what they referred to as “forced busing” wouldn’t work to bring about racial equality and would do nothing more than allow schools to meet quotas for racial diversity.

White parents framed their opposition to busing as a civil rights issue. “They largely grab ahold of codewords: they say they’re against ‘busing’ and that they’re for ‘neighborhood schools’ as a way to maintain the status quo of education in their cities,” Delmont says.

He adds that there were some black people who also criticized busing, but for different reasons: they wanted to see a deeper investment in black schools, teachers, and communities, rather than have black students sent to previously all-white schools that were often hostile to their presence.

Busing programs in Northern states attracted some of the fiercest criticism

Busing programs weren’t opposed just in Southern states. In fact, they were often met with even more resistance in the North. In addition to the aforementioned protests in New York in the 1950s, busing was heavily criticized in Detroit, for example, where white families boycotted it in 1960 and continued to oppose it in the years after. In Boston, politicians campaigned and won on anti-busing platforms, arguing that black students’ struggles to access a quality education and succeed in schools were not affected by segregation, but were instead the result of pathology. The city also saw a series of violent riots in the 1970s after schools were ordered to desegregate by a court.

“Busing becomes a very effective way of advancing desegregation in schools,” Brett Gadsden, an associate professor of history at Northwestern University and the author of Between North and South: Delaware, Desegregation, and the Myth of American Sectionalism, told Vox. “And because it was so effective, it became such a target for anti-busing activists.”

As opposition continued, anti-busing proponents argued that their criticism of busing was not opposition to school desegregation as a whole, and much of the media attention to and coverage of busing focused on white parent’s arguments that the practice was inconvenient and burdensome for children. But what this coverage ignored was that in districts that had been the most resistant to integration, the absence of busing programs would leave many schools segregated.

Critics of court-mandated school desegregation were assisted by lawmakers and legislators who argued that Northern states weren’t segregated intentionally but were rather just “racially imbalanced,” a framing that ignored how policy in many of these states was used to keep white people separated from African Americans. While the Civil Rights Act of 1964 used federal power and funding to enforce desegregation in the South, provisions that would have required stronger desegregation efforts in northern states were stripped out of the legislation. Even so, many northern cities would later find themselves subjected to court-ordered desegregation mandates that were strongly opposed.

Here’s how Delmont explained things in a 2016 Atlantic article on the history of opposition to busing in Boston:

With busing, Northerners had found a palatable way to oppose desegregation without appealing to the explicitly racist sentiments they preferred to associate with Southerners. “I have probably talked before 500 or 600 groups over the last years about busing,” Los Angeles Assemblyman Floyd Wakefield said in 1970. “Almost every time, someone has gotten up and called me a ‘racist’ or a ‘bigot.’ But now, all of the sudden, I am no longer a ‘bigot.’ Now I am called ‘the leader of the antibusing effort.’” White parents and politicians framed their resistance to school desegregation in terms like “busing” and “neighborhood schools,” and this rhetorical shift allowed them to support white schools and neighborhoods without using explicitly racist language.

As cities like Boston protested busing, lawsuits led to Northern cities being subjected to busing programs in the late ’60s and 1970s (the use of court-ordered busing was also upheld by the Supreme Court’s 1971 decision in Swann v. Charlotte-Mecklenburg Board of Education).

And in the mid-1970s, early into Biden’s first term as a US senator from Delaware, a part of his home state soon found itself facing the prospect of such an order.

Busing was one of the first issues to define Joe Biden’s early political career

In 1974, a federal court panel ruled that state housing and education policies had been used to keep the school systems of the city of Wilmington, Delaware (which was predominantly black), and its predominantly-white suburbs segregated. The court had not yet ruled that a busing program must be implemented, but white suburbanites still panicked over the prospect of having to follow a busing plan.

It presented a challenge for Biden, who had supported busing during his 1972 campaign against two-term incumbent Republican Senator J. Caleb Boggs, with Biden including busing as just one part of a larger commitment to uphold the Brown ruling and the Civil Rights Act. But after narrowly winning election to the Senate, in 1973 and 1974, Biden began to vote for anti-busing measures after feeling pressure from his constituents.

In one exception highlighted by the Biden campaign in recent days, he voted in 1974 against the Gurney Amendment, an anti-busing measure that would have ended the federal court’s ability to use busing plans, and would have also affected other court-ordered desegregation efforts. Biden cast the deciding vote on the measure, ending the amendment’s path forward in the Senate.

But while the Biden campaign has presented this as an example of the former senator’s allowance of busing, at the time Biden said he opposed the legislation for other reasons. It “would have allowed anyone affected by a civil rights decision from 1954 onward to re-open their court case,” Biden said of the amendment during a 1975 television interview. “Ninety percent of those cases had nothing to do with busing. It would have created havoc in our court system.”

He added that busing was an “asinine concept, the utility of which has never been proven to me.”

But even though Biden’s vote had nothing to do with his desire to preserve busing, his constituents were still outraged. As Delaware faced the looming prospect of a formal busing mandate, voters pushed Biden to take a stronger stance against busing. Biden did so, going on to vote for eliminating policies that would provide federal oversight of busing.

“Biden in some theoretical sense was in support of school integration,” says University of New Hampshire historian Jason Sokol, who wrote a 2015 Politico article on Biden’s busing record. But after seeing how angry his constituents were, Biden “fashions a politically expedient stance where he could claim he supports integration while opposing busing, which was the means to bring that integration.”

In 1975, shortly after Boston residents protested and rioted over the city’s desegregation order, Biden came out in favor of an amendment introduced by North Carolina Sen. Jesse Helms, a staunch opponent of civil rights legislation and desegregation efforts. Helms’s amendment would bar the then-active Department of Health, Education, and Welfare from collecting data about the race of students or teachers, and also prevented the department from requiring schools “to classify teachers or students by race.” Helms proudly announced that the measure would effectively end any federal oversight or enforcement of busing.

“I have become convinced that busing is a bankrupt concept,” Biden said as he stood to support Helms’s amendment. He added that the Senate should instead focus on “whether or not we are really going to provide a better educational opportunity for blacks and minority groups in this country.” Helms responded by welcoming Biden “to the ranks of the enlightened.”

The Helms amendment was defeated, but Biden then introduced a similar amendment. Here’s how Sokol described Biden’s proposal:

Biden proposed his own amendment to the $36 billion education bill, stipulating that none of those federal funds could be used by school systems “to assign teachers or students to schools … for reasons of race.” His amendment would prevent “some faceless bureaucrat” from “deciding that any child, black or white, should fit in some predetermined ratio.” He explained, “All the amendment says is that some bureaucrat sitting down there in HEW cannot tell a school district whether it is properly segregated or desegregated, or whether it should or should not have funds.” Finally, Biden called busing “an asinine policy.”

The measure passed, outraging Massachusetts Republican Edward Brooke, who at the time was the only black senator in Congress. Brooke called the Biden amendment “the greatest symbolic defeat for civil rights since 1964.” Biden later introduced a second amendment that explicitly barred the Department of Health, Education, and Welfare from ordering busing, but left other integration measures intact.

The second amendment easily passed the Senate, but both of Biden’s proposals were stripped out of the bill later in the process.

The measure marked a shift in how Biden, joined by some Democrats, would approach anti-busing legislation. “More than any other Northern Democrat, [Biden] adopted the language of conservatives on the issue, using terms like ‘forced busing’ when his fellow liberals would emphasize desegregation, not transportation,” the New York Times notes.

Biden “gave cover to other liberals and moderates who were in the same sort of position of thinking that school integration was a good thing, but whose constituents oppose busing,” Sokol says.

Biden did not stop with that proposal. In the years that followed, the then-senator would cast other votes and propose other anti-busing legislation, often working across the aisle to do so. The New York Times described many of these votes in June:

Mr. Biden introduced another proposal in 1976 that blocked the Justice Department from seeking busing as a desegregation tool, and co-sponsored an amendment in 1977 that limited federal funding of busing efforts. He continued his efforts that year with a bill curbing court-ordered busing. In February 1982, he voted for an amendment to a Justice Department appropriations bill described as the “toughest anti-busing rider ever approved by either chamber of Congress.” A month later, he voted in favor of another amendment that allowed the Justice Department to participate in litigation “to remove or reduce the requirement of busing in existing court decrees or judgments.”

And on June 28, NPR reported on a recently unearthed 1975 interview where Biden said that if legislation failed, he would be open to using a constitutional amendment to end mandated busing.

Over the years, Biden came to embrace his position as an opponent of busing, continuing to propose measures even after Wilmington officially entered a busing program in 1978. “No issue has consumed more of my time and energies than the question of court-ordered busing of students to achieve integration in our public school system,” Biden said during a 1981 Senate hearing on busing and the 14th Amendment.

“The courts have taken it upon themselves to go beyond simply dismantling deliberate segregation as an illegal government policy,” he added. “They have gone on to attempting to force integration by reassigning students to achieve particular racial balances.”

As Biden pushed for anti-busing legislation, the school desegregation measure was losing federal support in other areas. In 1974, the Supreme Court’s ruling in Milliken v. Bradley held that districts that had segregated schools but did not intentionally separate students by race could not be forced into desegregation plans. The ruling largely meant that northern states could not be forced to integrate city and suburban school districts. Busing would largely fall from the federal spotlight by the late 1980s and early 1990s, as fewer legislators and courts actively pushed for measures supporting it.

Biden has maintained that his opposition to federally-enforced busing was correct

Over the past four decades, Biden has used a series of arguments to make the case that his stance on busing was the right one. He’s said that his opposition to busing was the result of a distinction between de facto segregation (unofficial segregation believed to have occurred “naturally”) and de jure segregation (segregation that was directly and intentionally enforced by law), adding that he was okay with busing only in the latter case.

On June 28, the Biden campaign pointed to a quote the then-senator gave in 1975 explaining his stance. “In cases where a school system has racially segregated by gerrymandering district lines or by other legalistic means, Biden said he supports desegregation by any legal means at hand — including busing,” the Wilmington News Journal reported at the time. “However, for school districts which are all white or all black ‘because of historical pattern not involving segregation practices disapproved by a court’ he is against busing.”

Biden also discussed his reasoning for opposing busing in the same 1975 TV interview where he discussed the Gurney Amendment. “The new integration plans being offered are really just quota-systems to assure a certain number of blacks, Chicanos, or whatever in each school,” Biden said at the time.

“That, to me, is the most racist concept you can come up with,” he added. “What it says is, in order for your child with curly black hair, brown eyes, and dark skin to be able to learn anything, he needs to sit next to my blond-haired, blue-eyed son. That’s racist!”

But historians argue that these comments ignore the fact that by the 1970s and ’80s the lines on the issue were not as clearly drawn as Biden says. “He’s muddied his record a bit,” Sokol says. “The question is about where he stands on mandatory busing. The answer is that he became one of the leaders of anti-busing legislation in the Senate.”

Biden has also noted that he faced political pressure back home to oppose busing, and that his constituents actually called for him to go even further. Rather than busing, he said that the government needed to focus on reducing residential segregation and improving conditions in black communities, measures that are undoubtedly helpful, but would take much longer to implement than a busing program.

In interviews with Vox, historians argued that Biden’s framing of the issue is inaccurate, noting that busing orders successfully integrated many schools and that the use of busing to immediately reduce segregation did not prevent other integration efforts from being adopted.

“It’s a false dichotomy,” Delmont explains, noting that court-ordered desegregation occurred only when there was significant proof that a district was denying the constitutional rights of black students. Still, he says that Biden’s position “was popular among politicians, parents, and school officials as a way to oppose school integration, particularly in places outside of the South.”

Another argument made by Biden is simply that busing did not work. And if this is only a comment on busing as a political issue, he may be right. A 1973 Gallup poll of more than 1,500 adults found that just 5 percent of those surveyed said that busing was the best way to achieve integration. Other polls found more support for busing, a 1981 Gallup poll for example, found that 60 percent of African Americans and 17 percent of whites supported using busing to promote integration. But it is true that there was never a groundswell of national support for busing and whites overwhelmingly opposed it.

Still, experts and education journalists say that measuring the success of busing by its popularity is misguided and ignores that fact that desegregation measures as a whole were usually unpopular. And there’s been evidence that school desegregation, which was often achieved through busing, had powerful positive impacts on black students.

Research from Rucker Johnson, an economist at the University of California, Berkeley, has found that attending integrated schools led to better educational, health, and earnings outcomes for black students, and didn’t negatively impact white students. A 2007 paper from the National Bureau of Economic Research that examined school desegregation in Louisiana found that another benefit of desegregation was that funding for formerly all-black schools increased as districts prepared for white students to attend these schools. The paper concluded that for many black students, “the increased funding that came with desegregation was more important than the increased exposure to whites.”

Still, there were some negative consequences. One of the most commonly cited is that black teachers were often pushed out of jobs as schools closed in black communities. And some black parents chafed at the fact that their children were forced to bear the brunt of integrating schools. But even in these instances, “it wasn’t busing itself [that was the problem],” Delmont says. “It was the was that busing played out [in a way] that didn’t share burdens equally.”

Biden says his stance on busing isn’t controversial. His critics disagree.

Speaking to Vox in June, an adviser to the Biden campaign argued that Biden’s comments had been misconstrued to suggest that he opposed busing in its entirety, when he actually only opposed federal enforcement of busing in certain districts.

On June 28, addressing the renewed controversy over his busing record since the debates, Biden told the audience during an appearance at the Rainbow PUSH Coalition Convention in Chicago, “I want to be absolutely clear about my record and position on racial justice. I never, never, ever opposed voluntary busing.”

But for some, that claim is simply a distinction without a difference. “He wasn’t just a silent supporter of anti-busing, he was out there crafting bills,” Noliwe Rooks, a professor of Africana studies and director of American studies at Cornell University, told EdWeek recently. “As a standalone, [his opposition to busing] probably wasn’t going to be that big a deal. But when you put that in tandem with his more recent comments about these white segregationists, it’s a problem.”

In recent weeks, Biden’s campaign has tried to move past the busing discussion by highlighting the former vice president’s record supporting other civil rights legislation. His campaign is also pointing to Biden’s strong relationship with older black activists in Delaware, with many of these activists arguing that criticism of Biden is misplaced and that he was right to oppose busing in the state.

Harris’s criticism of Biden’s record has also called attention to her own stance, sparking criticism that she doesn’t actually seem to support federal enforcement of busing orders either. Early in July, she told reporters that the matter should be left to local governments. A day later, Harris said that the government should intervene only when a district has failed to integrate. (It’s worth noting that pursuing busing programs would be much more difficult today due to the Supreme Court’s 2007 Parents Involved ruling, which limited school districts’ ability to consider race when assigning schools).

And on July 12, Politico reported that Biden supports congressional efforts to remove a decades-old anti-busing provision barring schools from using federal money on voluntary busing programs. But given that Biden has always reserved his opposition for court-ordered busing programs, this doesn’t really suggest any change in Biden’s prior stance on busing.

While questions about Biden’s record on busing continue to circulate in the news, it’s still unclear if the issue will actually resonate with voters in general, or Biden’s base of black support in particular. Polling in the aftermath of the debates have shown Biden’s numbers fall with black voters, as Harris has surged, but it will take time to see if these numbers show any sort of lasting change to either candidate’s support.

The debate over busing has the potential to spark a much larger political discussion of how to address school segregation. But experts caution that any serious discussion of school desegregation in 2019 will need to include much more than asking candidates about modern-day busing programs.

Gadsden, the Northwestern historian, argues that this conversation needs to acknowledge the fact that school segregation — and the educational inequality that came with it — has long been treated as normal in American education. There’s a sort of “willed amnesia about the inherently unequal quality of segregated education in America,” he says.

And for Biden specifically, one thing that does seem apparent is that his primary opponents see weakness in this part of his record — especially when coupled with the controversy over Biden’s comments about segregationist senators and his role in the passage of the 1994 crime bill. At times, discussion of Biden’s lead in primary polling has treated his campaign as if it was unstoppable. Harris showed at the first debate that his image can be bruised.