(Bloomberg) -- The US Supreme Court upheld a Republican-drawn congressional map in South Carolina, rejecting claims of racial gerrymandering and boosting the GOP in the fight to control the House for the rest of the decade.

Voting 6-3 along ideological lines, the justices overturned a lower court’s finding that lawmakers unconstitutionally relied on race when they drew what is now a Republican-held district. The high court majority said the challengers hadn’t shown that race was the driving factor, rather than permissible partisan considerations.

Although the Republican-drawn districts were already set to be used this year’s elections, the ruling all but ensures they will stay in effect until the next round of redistricting after the 2030 census.

A three-judge panel concluded that lawmakers established a target of 17% Black voters in South Carolina’s 1st District, shifting tens of thousands of African Americans out of the district to hit the goal. The configuration left the GOP with a comfortable majority in the Charleston-based district, which elected Republican Representative Nancy Mace in 2022

Writing for the Supreme Court majority, Justice Samuel Alito said the state had “strong evidence” that the 17% figure “was simply a side effect of the legislature’s partisan goal.” 

He added: “And certainly nothing rules out that possibility. In light of the presumption of legislative good faith, that possibility is dispositive.”

Kagan Dissent

The ruling underscores the difficulties voters will face going forward in pressing claims of racial gerrymandering, given the close correlation between race and politics in many parts of the country. Under a 2019 Supreme Court ruling, lawmakers have a free hand under federal law to draw lines for purely partisan reasons.

Dissenting Justices Elena Kagan, Sonia Sotomayor and Ketanji Brown Jackson blasted the ruling as giving states an unwarranted advantage when they are accused of drawing voting districts along racial lines.

“In every way, the majority today stacks the deck against the challengers,” Kagan wrote for the group. “When racial classifications in voting are at issue, the majority says, every doubt must be resolved in favor of the state, lest (heaven forfend) it be ‘accused’ of ‘offensive and demeaning’ conduct,” she added, quoting from Alito’s opinion.

Alito also faulted the challengers for not offering an alternative map to show how the state could have achieved its aims without relying so heavily on race.

Justice Clarence Thomas, who joined the majority, wrote separately to say federal courts shouldn’t even consider claims that voting lines are unconstitutional. “Drawing political districts is a task for politicians, not federal judges,” he wrote.

The issues were different from those the justices addressed last year, when the court said Alabama Republicans violated the Voting Rights Act with a congressional map that contained only one majority-Black district. The South Carolina fight concerned a separate line of Supreme Court cases that say the Constitution’s equal protection clause bars people who draw maps from making race the “predominant” factor.

Both sides had asked the high court to rule by the end of 2023 to allow time to finalize a map for this November’s election. But when the justices still hadn’t ruled by late March, the lower court panel said it was too late to change the map for 2024, ordering use of the Republican-drawn lines even though the judges had found those districts to be unconstitutional.

Since South Carolina picked up a seventh congressional district after the 2010 census, Republicans have held a 6-1 majority every election cycle except for one. Democrat Joe Cunningham won the 1st District in 2018, before losing to Mace two years later.

The case is Alexander v. South Carolina State Conference, 22-807.

(Updates with excerpts from opinions starting in fifth paragraph.)

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