The Supreme Court on Wednesday told a lower court to reexamine the redistricting efforts of Virginia’s Republican-led legislature for signs of racial bias and gerrymandered legislative districts that dilute the impact of African American voters.

The justices declined to take a position on that issue. But they said a lower court had not applied the right standards when it concluded that the legislature’s work was constitutional.

[Supreme Court hears arguments in Virginia redistricting case ]

The decision was a win for black voters and Democrats who have challenged the General Assembly’s actions in drawing legislative as well as congressional lines.

A win at the Supreme Court last term resulted in redrawing the congressional map in a way that favored the election of a second African American congressman last fall.

It is unclear whether Wednesday’s technical and splintered decision would have such an impact or even whether any changes would be made in time for the fall elections.

[Supreme Court agrees Virginia congressional districts must be redrawn]

But the decision buoyed Democrats, who are making a push to field candidates in most, if not all, of the 100 seats of the House of Delegates that are up for election.

The court ruling “contributes to the momentum that the Democrats believe they might finally have in actually being far more competitive in the Assembly elections this year than they have previously,” said longtime Virginia political analyst Bob Holsworth. “The redistricting case is on top of sort of the mobilization the Democrats are seeing in their local meetings, the increased attendance, the interest in actually running for election that you’re seeing among more people.”

House Speaker William J. Howell (R-Stafford) said he was disappointed in the ruling but played down its significance.

“The Supreme Court declined the plaintiffs’ request to find that the districts are unconstitutional,” Howell said. “The Supreme Court overruled the way in which the district court analyzed the case. We have read the court’s opinion and are quite confident that we will win when we go back to the district court.”

Justice Anthony M. Kennedy, writing for five other justices, said the three-judge panel that initially considered the challenge made a mistake in its examination of Virginia’s districts.

Under Supreme Court precedents, the maps can sometimes require an examination of race to make sure minorities have a chance to elect candidates of their choice. But race cannot be the predominate factor in drawing districts. In Virginia and other states, challengers have said Republicans have packed minorities into a small number of districts to make surrounding areas more hospitable to GOP candidates.

The lower court held that if traditional redistricting practices such as compactness and protecting incumbents could explain a district, then race could not have been the predominant reason for their creation.

But Kennedy said courts must look at the real reason for drawing the district, not whether it could be justified by other means.

“A state could construct a plethora of potential maps that look consistent with traditional, race-neutral principles,” Kennedy wrote. “But if race for its own sake is the overriding reason for choosing one map over others, race still may predominate.”

Chief Justice John G. Roberts Jr. and Justices Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan joined Kennedy’s opinion. Justice Samuel A. Alito Jr. mostly concurred, and Justice Clarence Thomas repeated his disapproval of using race to draw legislative districts, whether it predominates or not. Voting law experts disagreed about the decision’s impact. Richard Hasen, an election law expert at University of California at Irvine, said the ruling was technical and did not greatly expand the court’s precedents.

New York University law professor Richard Pildes disagreed. “The court’s opinion today is more forceful and clear than it has ever been that unconstitutional racial gerrymandering can occur even when a state draws districts that look regular and follow traditional districting principles,” he wrote in a blog post.

Marc E. Elias, who represented the challengers, said the decision will make it easier to win when the lower court reconsiders the 11 districts at issue. Its previous decision shut down efforts to show that Virginia was able to “hide the racial gerrymandering in districts that don’t look bizarre,” he said.

The Supreme Court upheld one district that was disputed, saying the legislature had made the case that it needed a black voting age population of 55 percent in order for a minority candidate of choice to prevail.

The House districts are in Richmond, the Hampton Roads area and along the state’s southern border. All have African American voter majorities.

In the House, where Republicans were in charge when the legislative districts were redrawn after the 2010 Census, Democrats are outnumbered 66 to 34. (In the Senate, where Democrats were in control at the time of reapportionment, the GOP has a 21 to 19 advantage.)

Democrats have already announced candidates in 75 House districts this year, and they are counting on national attention — and money — as they cast their races as referendums on President Trump.

It is unclear if the case could play out before the November elections. But if the lower court rules that boundaries have to be redrawn at any point after that, Virginia would have to call special elections. Aside from the 11 districts affected by this case, an additional five are being litigated in Richmond Circuit Court, where a redistricting advocacy group has challenged them as being too sprawling to meet federal standards of compactness. That hearing is set for later this month.

If all the districts in both cases were found to be unconstitutional, they and the ones around them would have to be redrawn. That could amount to 30 districts or more in total — roughly a third of the Virginia House, said Brian Cannon, executive director of One Virginia 2021, the redistricting advocacy group that filed the Richmond case.

The decision came in Bethune-Hill v. Virginia State Board of Elections.

Schneider reported from Richmond.