The justices in a 6-3 decision, with the conservative justices in the majority and liberal justices dissenting, reversed a lower court's ruling that the Republican-drawn map violated the rights of Black voters under the U.S. Constitution's 14th Amendment, which guarantees equal protection under the law. The Supreme Court's ruling was authored by conservative Justice Samuel Alito.
The court's liberal justices issued a sharply worded dissent, expressing alarm at the decision to raise the bar to prove that an electoral map racially discriminates in violation of the Constitution.
"What a message to send to state legislators and mapmakers" who often have incentives to use race to achieve partisan ends, or to suppress the electoral influence of minority voters, liberal Justice Elena Kagan wrote. "Go right ahead, this court says to states today."
The lower court on March 28, because of the length of time it took the Supreme Court to act, decided that the disputed map can be used in this year's congressional elections, a ruling that could undercut Democratic chances of winning control of the U.S. House of Representatives.
The conservative majority on Thursday sided with South Carolina Republicans who argued that the state's first congressional district map was designed to secure partisan advantage, a practice that the Supreme Court in 2019 decided was not reviewable by federal courts - unlike map-drawing that is mainly motivated by race, which remains illegal.
The majority found that the NAACP civil rights group and Black voters who challenged the map failed to prove that the map's design was chiefly motivated by race.
This case was being closely watched ahead of the Nov. 5 U.S. election in which the presidency and control of both chambers of Congress will be decided. Democrats lost their majority in the 435-seat House in the 2022 election and are hoping to overcome the slim Republican majority this year, with every competitive district crucial to the outcome.
Republicans hold a 217-213 margin in the House.
Ongoing legal battles over redistricting in several other states could be enough to determine control of the House in the election.
The South Carolina legal fight centered on a map adopted in 2022 by the Republican-led state legislature that redrew the boundaries of one of the state's seven U.S. House districts - one that includes parts of Charleston along the Atlantic coast.
Alito wrote that "no direct evidence supports the district court's finding that race predominated in the design of District 1," and that "circumstantial evidence falls far short of showing that race, not partisan preferences, drove the districting process."
The lower court took a "misguided approach" to resolving the case, including the evidence it relied on and by "paying lip service" to the assumption that the legislature acted in good faith, Alito wrote.
A federal three-judge panel in January 2023 ruled that the map unlawfully sorted voters by race and deliberately split up Black neighborhoods in Charleston County in a "stark racial gerrymander."
Gerrymandering is a practice involving the manipulation of the geographical boundaries of electoral districts to marginalize a certain set of voters and increase the influence of others. In this case, the state legislature was accused of racial gerrymandering to reduce the influence of Black voters, who tend to favor Democratic candidates.
Kagan said the electoral sorting based on race will continue as a result of Thursday's ruling: "We should demand better - of ourselves, of our political representatives, and most of all of this court." Kagan said the ruling "thwarts efforts to undo a pernicious kind of race-based discrimination," and is "meant to scuttle gerrymandering cases."
The boundaries of legislative districts across the country are redrawn to reflect population changes measured by the census conducted by the U.S. government every decade. In most states, redistricting is done by the party in power.
The new map in South Carolina increased the district's share of white voters while reducing its share of Black voters, which the lower court referred to as "bleaching."
The map shifted 30,000 Black residents who had been in the 1st congressional district into the neighboring 6th congressional district, which stretches 125 miles (200 km) inland from Charleston. These voters were unlawfully "exiled," the three-judge panel wrote.
The 6th district has been held for three decades by Democrat Jim Clyburn, one of the most prominent Black members of Congress. Clyburn's is the only one of South Carolina's House districts held by a Democrat.
With the district's previous boundaries in place, Republican Nancy Mace only narrowly defeated an incumbent Democrat in 2020 - by just over 1 percentage point, or 5,400 votes. With the redistricting, Mace won re-election in 2022 by 14 percentage points.
