UPDATED. This post has been updated after a Harris Senate spokesperson said Friday afternoon that she supports the Strength in Diversity Act.

An intense dispute between former Vice President Joe Biden and Sen. Kamala Harris about segregation in education and how Washington should address it highlighted the second night of the first debate among Democratic candidates for president.

In the second hour of Thursday’s 10-candidate debate, the California senator challenged Biden for what she called his opposition in the 1970s to busing as a strategy to help desegregated schools, a charge Biden rejected. The subsequent exchange underscored how racial segregation in education, as well as Biden’s ongoing defense of his relationship with segregationists in Congress decades ago, could prove to be a potent issue in the Democratic Party primary.

The Democratic candidates also stressed their support for the Deferred Action for Childhood Arrivals program, a 2012 executive order signed by President Barack Obama that provides legal protections for nearly 700,000 undocumented immigrants, including thousands of public school students and teachers.

Otherwise, they mostly brushed lightly over K-12 policy topics. Biden did emphasize his support for additional school aid. And a few candidates also used gun violence at schools to push for additional restrictions on firearms.

‘I Did Not Oppose Busing in America’

Harris sparked the most noteworthy discussion about education when she turned her attention to Biden, saying that as a senator he had an overly cozy relationship with segregationists on Capitol Hill and that he also worked with them to oppose busing. She then pointed out that as a child in Berkeley, Calif., she participated in a busing program, and that opposition to such a program was personally hurtful to her. Her social media team was ready for the moment:

After Biden denied Harris’ allegation that he had “praised racists,” Harris asked Biden directly if he would agree that he was wrong to oppose busing. Biden replied that Harris had mischaracterized his views, stating “I did not oppose busing in America. What I opposed is busing ordered by the Department of Education.” Harris reacted by highlighting the “failure of states to integrate public schools in America.”

The former vice president subsequently stressed that his position meant that Harris would still have been able to take advantage of busing because city officials had instituted it without federal intervention. (Berkeley’s school board voted to adopt its initial desegregation plan in 1964.) But the senator rejected this philosophy of leaving it to local communities to address segregation.

“That’s where the federal government must step in,” Harris shot back. “There are moments in history where states fail to preserve the civil rights of all people.”

While he voted against some anti-busing bills, Biden was considered a strong opponent of busing early in his Senate career. He proposed several measures, including riders that restricted the use of federal funding to pay for transportation for desegregation purposes, and a bill that would have limited the Department of Justice’s ability to propose busing as a remedy to segregation.

There is legislation in Congress to promote school diversity initiatives, including busing. It’s the Strength in Diversity Act, introduced this year by Sen. Chris Murphy, D-Conn., and Rep. Marcia Fudge, D-Ohio. It would provide grants to districts that want to address racial and socioeconomic diversity, including those who want to use a transportation plan to do so.

The bill has three cosponsors. Harris is not one of them. However, her office said Friday that Harris supports the bill.

Although controversy over school busing and desegregation in general has roiled schools for decades, it remains a salient point of discussion in ongoing debates about whether, and how, to focus on integrating schools. Washington has long prohibited schools from using federal money to implement transportation plans designed to promote integration. Although a recent federal spending bill rolled back part of the prohibition, advocates say the ban effectively remains on the books.

A bill passed by the House education committee this year would provide grants to districts seeking to use new transportation strategies to help integrate schools, among other things. However, the Supreme Court has ruled against desegregation efforts in cases such as Milliken v. Bradley and Parents Involved in Community Schools v. Seattle School District No. 1.

A 2016 federal report found that the share of schools in America that are racially isolated with high concentrations of students in poverty was on the rise. The Obama administration sought to encourage schools to put more weight on racial and socioeconomic diversity, but the Trump administration has scrapped these initiatives.

Immigration and DACA

Candidates at Thursday’s debate also made it clear that they oppose President Donald Trump’s attempt to undo the DACA program, which protects those who were brought to the U.S. illegally as children.

Harris said that in addition to preserving DACA for current recipients, she would extend DACA’s protections to their parents. And Sen. Bernie Sanders, I-Vt., put his support for DACA in the broader context of immigration policy: “We rescind every damn thing on this issue that Trump has done.”

Trump has sought to revoke DACA, but the latest legal action in the courts has upheld the program for now, meaning that those who have or previously had DACA protections can seek to renew them. The Supreme Court could ultimately decide to take up the issue. Efforts in Congress to enshrine DACA in statute have failed.

The Migration Policy Institute recently estimated that since 2012, 250,000 students have become eligible for DACA, and that DACA protects 9,000 teachers who are undocumented immigrants.

Disadvantaged Students and Early Learners

Biden also highlighted key elements of the plan for schools he released last month. In describing the need for people to be better prepared for higher education, Biden said, “That’s why I think we should triple the amount of money we spend for Title I schools. That’s why I think we should have universal pre-K.” (Biden wants to triple Title I aid to help boost pay for teachers.)

Such policies, along with focusing on continuing education, would also help prepare people for the jobs of the 21st century, Biden said. He didn’t define exactly what “continuing education” means to him. But advances in technology that drive automation could have a big impact on K-12 schools down the road.

President Barack Obama sought to dramatically expand access to early-childhood education for low- and middle-income students, including a signature proposal to create universal access to preschool using a federal-state partnership. That latter plan ultimately fell short.

Sanders has also pledged to triple Title I funding as part of his expansive K-12 plan.

Contrast With the First Night

As with the first night of the Democratic debate the previous evening, candidates used the 2018 school shooting 50 miles away in Parkland, Fla., to call for additional gun control measures.

Sen. Kirsten Gillibrand, D-N.Y., hailed those Marjory Stoneman Douglas High School students who have pushed for additional gun control, saying, “Imagine the Parkland kids having as much power as the Koch brothers or the NRA.” One of those activists, David Hogg, reacted to similar praise from Democrats on Wednesday by emphasizing the scope of the recent surge in gun-control activism:

And Rep. Eric Swalwell, D-Calif., highlighted the “thousands of black children killed in our streets” and the emotions of parents who memorize what their children wear on the way to school in case they need to identify their children later, after a shooting.

“We have to be a country where we love our children as much as we love our guns,” Swalwell said.