Rearguments are rare, and they can signal major upheavals.

The dispute centers on whether Louisiana lawmakers ran afoul of the Constitution when they adopted a new electoral map in 2024, creating the state’s second majority-Black district. If the justices decide that lawmakers cannot consider race in drafting maps, redistricting could result in congressional seats flipping from blue to red throughout the country.

Here’s what else to know:

• Three groups of voters: The legal battle reaches back to the 2020 census, which showed Black voters made up a third of the state. Lawmakers revisited the congressional map but maintained one majority Black district, out of the state’s six. Two groups of Black voters sued, arguing the map violated the Voting Rights Act. After another map was proposed including a second majority-Black district, a dozen white voters sued, arguing it was an illegal racial gerrymander.

• Voting Rights Act: The way the justices framed the reargument of this case suggests they may be considering holding the provision of the Voting Rights Act that has been used to challenge redistricting plans unconstitutional. Back in 2013, the court struck down the heart of the law.

• Revisiting the case: The justices heard arguments in this case last spring, but instead of issuing a decision, they scheduled a new argument this term. Rearguments of a Supreme Court case are rare, and a characteristic move of the court led by Chief Justice John G. Roberts Jr., one that has often paved the way for major legal changes.

• Repeated skepticism: The Voting Rights Act has faced legal challenges, and skepticism from the Supreme Court, since it was signed into law by President Lyndon B. Johnson in 1965.

J. Benjamin Aguiñaga, Louisiana’s solicitor general, is also making a repeat appearance on behalf of the state, even though he is no longer defending the disputed map. Mr. Aguiñaga also appeared before the court two years ago, representing Louisiana and Missouri in an unsuccessful effort to restrict the Biden administration’s efforts to get social media companies to flag disinformation.

Hashim M. Mooppan, a principal deputy solicitor general, is arguing in support of Louisiana and white voters, on behalf of the Trump administration. Mr. Mooppan last week appeared before the justices in support of a Christian therapist challenging Colorado’s law that prohibits the counseling of minors to change their sexual orientation or gender identity.

Janai Nelson, a lawyer and the president of the NAACP Legal Defense Fund, is making her debut before the Supreme Court. She will argue on behalf of a group of Black voters defending the Louisiana map that includes two majority Black districts, and for voting rights protections more broadly.

Civil rights lawyers’ worries about the Louisiana case turned into alarm in August, when the court instructed the parties to file supplemental briefs on whether Louisiana’s “intentional creation of a second majority-minority congressional district violates the 14th or 15th Amendments to the U.S. Constitution.”

The question can be read in several ways. But it certainly suggested that the court may consider holding that a main provision of the Voting Rights Act of 1965 is unconstitutional.

Ordering reargument or otherwise returning to a subject after an initial encounter is a characteristic move of the court led by Chief Justice John G. Roberts Jr., one that has often paved the way for legal upheaval.

In a pair of articles, Richard M. Re, currently a law professor at Harvard, called this the “doctrine of one last chance.” Before the justices take a major step, he said, they give signals that offer the affected parties and the nation time to respond, prepare and adjust.

“For example,” he wrote in 2014 in The Green Bag, a legal journal, “the Roberts court initially ducked constitutional challenges to central pillars of the Bipartisan Campaign Reform Act and the Voting Rights Act. But when those measures came before the court for a second time, they were both struck down as unconstitutional, despite their importance and bipartisan support.”

In a follow-up article in The U.C.L.A. Law Review in 2019, he said the Roberts court had executed a similar two-step in 2018 in overruling a precedent about public unions. The precedent had been severely criticized in earlier decisions, but the court had stopped short of overruling it.

As a result, Professor Re wrote, the 2018 ruling “managed to be both widely predicted and revolutionary.”

Both men are Democrats and flipped their respective seats. Both seats were also previously held by white men in two Southern states where at least a quarter of the population is Black.

Should the Supreme Court further gut the landmark civil rights law with its decision expected in the Louisiana case next year, those districts could be redrawn again, especially as Republicans look to boost their razor-thin majority in the House.

With Mr. Figures joining Representative Terri Sewell, the 119th Congress became the first in history in which Alabama was represented by two Black lawmakers. Mr. Figures has worked to build on the legacy of his father, a renowned civil rights lawyer, and his mother, Vivian Davis Figures, who has served in the State Senate for nearly 30 years.

Mr. Fields had walked the halls of Congress before on behalf of Louisiana voters, serving from 1993 to 1997. But a court then ordered the congressional map to be redrawn, eliminating his district.

Last year, after Republicans convened under court order to redraw the map, Mr. Fields, a state senator at the time, was able to successfully overcome a crowded primary field and return to Capitol Hill.

But Section 5 and preclearance are not the only national legacy of the law.

Section 2, at issue on Wednesday, has been used in states across the country, largely in cases in which people have claimed that they were discriminated against in voting laws or maps and that their voting power as members of minority communities was diluted. Between 1982 and 2005, Montana and South Dakota lost or settled more than five cases that hinged on Section 2, according to a New York Times study. New Mexico has lost or settled at least three cases.

A study by researchers at the University of Michigan found that between 1982 and 2021, there were 439 cases based on Section 2 that resulted in published decisions or opinions available on legal websites. About 200 of those cases came from states outside of the South.

“It kind of speaks to the magnitude of the geographic impact that the Voting Rights Act had, because even beyond preclearance, there have been Voting Rights Act suits in lots of other parts of the country,” said Justin Levitt, a law professor and voting rights expert at Loyola Marymount University.

While Section 2 cases have been brought against statewide laws and have been used to challenge the boundaries of congressional districts, the provision is often used more at the local level, such as by city councils, state legislatures and school boards.

In New York in 2017, civil rights groups incorporated Section 2 by arguing that the system of electing members to the school board of the East Ramapo Central School District in diverse Rockland County prevented Black and Latino communities from choosing members of their choice. In 2020, a federal court agreed.

Section 2 claims have been particularly critical for Native American populations. In one case, Turtle Mountain Band of Chippewa Indians v. Michael Howe, the plaintiffs argue that the North Dakota state legislative map diluted the voting power of Native Americans. (The Supreme Court is now considering whether to accept the case, not on the merits of the arguments, but to weigh whether private groups and people — as opposed to the government — can sue under the Voting Rights Act.)

The law has also helped expand voting access. In 2020, the Blackfeet Nation, a reservation in Montana larger than Delaware, successfully brought a Section 2 claim against the state for only having four ballot drop-off locations across the reservation.

The justices sided with Ms. Shaw in a 5-to-4 decision, setting a precedent that race alone could not be the basis for redrawing district lines. That ruling set in motion a series of challenges to other majority-Black districts in Texas, Louisiana, Florida and Georgia.

Justice Sandra Day O’Connor, who wrote the majority opinion, said a district that includes voters of the same race but who are “otherwise widely separated by geographical and political boundaries, and who may have little in common with one another but the color of their skin, bears an uncomfortable resemblance to political apartheid.”

Twenty years later, in 2013, came Shelby County v. Holder, with its fatal blow to the provision of the Voting Rights Act that had required that states like Louisiana and Alabama get preapproval from the Justice Department before changing their election laws.

By then, Chief Justice John G. Roberts Jr. had joined the court. His skepticism of the Voting Rights Act dated at least as far back as his time as a young lawyer in the Reagan Justice Department, when, as a special assistant to the attorney general, he wrote a series of memos that later became public aggressively pushing back on a bipartisan proposal to shore up the expiring Voting Rights Act.

In 2021, in Brnovich v. Democratic National Committee, the justices agreed that the Voting Rights Act prohibited only laws or policies that imposed such substantial and disproportionate burdens on minority voters that it effectively stopped them from casting ballots.

After years of chipping away at the act, the Supreme Court took a surprising turn in 2023 in a fight over Alabama’s voting map. In an opinion written by the chief justice, a majority of the court upheld the court’s precedent that race could play some role in redistricting if it was intended to ensure that minority voters would not have less opportunity than members of the majority to participate in the political process.

Another of the court’s conservatives, Justice Brett M. Kavanaugh, joined the majority. But he cautioned in a concurrence that the finding might be temporary, warning “the authority to conduct race-based redistricting cannot extend indefinitely into the future.”

When the challenge to Louisiana’s voting map arrived at the court, it appeared to be a narrow fight over whether lawmakers had relied too much on race, rather than politics, when they drafted the state’s congressional map that includes two majority Black districts.

The justices heard oral argument in March. But instead of announcing an opinion in the summer, as is typical in major cases, the justices made the rare move of scheduling the case to be reargued. Weeks later, they announced they wanted the new argument focused on the new, broader question of whether considering race in redistricting is unconstitutional.

Since then, court watchers have puzzled over the role this Louisiana case might play in the arc of the voting law.

But the majority opinion written by Chief Justice John G. Roberts Jr. in the Shelby County case said another part of the law, its Section 2, would remain in place to protect minority voting rights. It allows lawsuits challenging election maps and other voting procedures — but only after they take effect.

“Section 2 is permanent, applies nationwide and is not at issue in this case,” he wrote.

In dissent, Justice Ruth Bader Ginsburg said Section 2 was not nearly as valuable as Section 5.

“Litigation occurs only after the fact, when the illegal voting scheme has already been put in place and individuals have been elected pursuant to it, thereby gaining the advantages of incumbency,” she wrote. “An illegal scheme might be in place for several election cycles before a Section 2 plaintiff can gather sufficient evidence to challenge it. And litigation places a heavy financial burden on minority voters.”

Even so, civil rights lawyers say the provision is a lot better than nothing. But it may now be in peril.

In June, the court surprised observers by calling for another round of arguments in a voting rights case from Louisiana. Then, in August, it instructed the parties to address an additional question, one that suggested the court may hold Section 2 unconstitutional. That discussion is expected to dominate the argument on Wednesday in front of the justices.

Civil rights lawyers have a particular reason to be wary of Chief Justice Roberts. When he was a young lawyer in the Reagan administration, he unsuccessfully worked to oppose the expansion of Section 2, which had initially covered only intentional discrimination, to address practices that had discriminatory results.

But the case could have much broader implications for the law and for politics, potentially gutting the remaining pillar of the Voting Rights Act of 1965, which the Supreme Court’s conservative majority has sharply curtailed in recent years. If the justices decide that lawmakers cannot consider race in drafting maps, redistricting could result in congressional seats flipping from blue to red throughout the country.

The legal battle can be traced back to the 2020 census, which showed an increase in Louisiana’s population of Black adults. While Black Louisianans made up about a third of the state’s population, there was only one majority-Black congressional district out of six districts.

After the census, state lawmakers revisited the map and passed a version that still had only one majority-Black district. Two groups of Black voters then filed federal lawsuits in 2022, asserting that state legislators had violated the Voting Rights Act by packing Black voters into one district and diluting their voting power.

The Voting Rights Act, one of the central legislative achievements of the civil rights movement, banned discriminatory practices like literacy tests that had been used to disenfranchise people. It also prohibited measures aimed at denying minority voters an equal opportunity to elect candidates of their choice.

A federal judge agreed, finding that the map likely did violate the statute. State lawmakers then proposed another map in January 2024, which included a second majority-Black district — a long, narrow one that wound from the southeast part of the state to the northwest.

State lawmakers claimed that they had crafted the map with politics, not race, in mind, protecting valuable Republican incumbents, including Speaker Mike Johnson.

But shortly after lawmakers approved that map, a dozen white voters sued, arguing that the new map was an illegal racial gerrymander that had caused them to suffer “unlawful, intentional discrimination based on race.”

In April 2024, a divided panel of three federal judges agreed, striking down the new map. Louisiana then appealed to the Supreme Court. The justices paused the lower court’s order, allowing Louisiana’s new map to be used in the 2024 election. Democrats picked up a seat, as voters in the newly created district elected Cleo Fields, a longtime party figure from Baton Rouge. Mr. Fields is Black.

The justices heard the case, Louisiana v. Callais, in the spring. But instead of issuing a decision in late June or early July, the justices, in a rare move, ordered new arguments for their next term, which began this month. Rearguments can be a signal that the justices are poised to take a broader action in a case. In 2009, the court called for reargument in Citizens United, a campaign finance case that turned from a minor case into a blockbuster, clearing the way for unlimited campaign spending by corporations.

The court offered no explanation for punting on the case, but several weeks later, the justices announced that they would hear arguments on a more expansive question: whether Louisiana’s “intentional creation of a second majority-minority congressional district violates the 14th or 15th Amendments to the U.S. Constitution.”

That question suggested that the justices appeared to be considering holding the provision of the Voting Rights Act that has been used to challenge redistricting plans unconstitutional.

The court’s conservative justices have long pointed to what they have viewed as a tension between the Voting Rights Act’s goal of protecting minority voting rights and a colorblind conception in the 14th Amendment’s equal protection clause, which requires that the law treat everyone equally.

Two years ago, however, the justices rejected an Alabama voting map, finding that it had diluted the power of Black voters. In that case, Chief Justice John G. Roberts Jr., who has been a skeptic of the Voting Rights Act for decades, wrote the majority opinion agreeing that lawmakers could take race and other factors into account when redistricting.

The new question in the Louisiana case has shaken up the alliances from the first argument.

In the months since the justices announced that they would hear arguments again, the Louisiana officials who had defended the map have essentially switched sides, aligning with the white voter plaintiffs. They are joined by lawyers for the Trump administration.

In a brief to the court, Liz Murrill, Louisiana’s attorney general, described the structure of the provision of the Voting Rights Act that allows race to be used as a factor in redistricting — Section 2 — as “unworkable and unconstitutional.”

“Race-based redistricting under Section 2 is principally unconstitutional because it inherently rests on a racial stereotype: that all voters of a particular race must — by virtue of their membership in their racial class — think alike, share the same interests and prefer the same political candidates,” she wrote.

The constitutionality of Louisiana’s second majority-minority district is now being defended by the NAACP Legal Defense Fund, the American Civil Liberties Union and other voting rights organizations. These groups have argued that the case is about whether minority communities continue to have meaningful representation in politics. They have also raised concerns that gains from the civil rights era were at risk.

In a brief to the court, the civil rights and voting groups asserted that the country had made strides toward racial equality in the decades since the Voting Rights Act was signed into law, but that it was the wrong moment to unravel protections and return to what they called “a blinkered past.”

The groups argued in their brief that Louisiana was taking a “burn-it-all-down approach” that could usher in problems seen before the Voting Right Act.