Mary Jo Pitzl

The Republic | azcentral.com

In a unanimous decision, the U.S. Supreme Court upheld Arizona's legislative map, ruling the state's Independent Redistricting Commission did not violate the principle of one-person, one-vote when it created new boundaries.

The justices on Wednesday rejected a challenge from a group of Republican voters who claimed the commission illegally packed GOP voters into some districts while leaving other Democratic-leaning districts with smaller populations.

The 8-0 ruling means Arizona's legislative boundaries, which have been in use since 2012, will remain intact through the end of the decade.

In a statement, the commission's director applauded the decision and said the panel is "gratified" the district lines will remain intact. An adverse ruling could have sent the commission, or a court, scrambling to redraw the map in time for the Aug. 30 primary.

The court's ruling comes after a federal appeals court upheld the new boundaries in 2014 after finding that the commission was trying to comply with a now-nullified provision of the Voting Rights Act. The provision required federal pre-clearance before the map could proceed, in an effort to protect minority voting rights.

Critics argued the commission was motivated by partisanship, resulting in too many Democratic-leaning districts when demographics would suggest a smaller number should tilt toward Democrats.

Writing for the court, Justice Stephen Breyer said the one-person, one-vote principle “does not demand mathematical perfection.”

Joe Kanefield, who represents the commission, said he was pleased with the ruling and, based on the questions the justices asked during a December hearing, not surprised by the outcome.

"Partisanship was not the commission's goal," Kanefield said. "It's only been about pre-clearance."

Wes Harris, the lead plaintiff in the case, did not immediately return a call seeking comment

Redistricting returns to U.S. Supreme Court: Here's what to know

The Supreme Court requires a state’s legislative districts to have roughly equal numbers of people, but it has long said those numbers don’t have to be exact. Differences of less than 10 percent are presumed constitutional unless challengers can show they are the result of discrimination or other invalid reasons.

In Arizona, the average population difference in redrawn districts was 2.2 percent, with a maximum difference of 8.8 percent. The plan placed more Republican voters in some districts that already were likely to elect GOP candidates and left other districts with smaller overall populations. Those districts have a greater concentration of Hispanic voters and are considered more likely to vote for Democrats.

In the two election cycles since the maps have been in place, they have produced exactly the same partisan split at the Legislature: 36 Republican seats in the House and 24 for Democrats; and a 17-13 split in the state Senate. However, last year, Sen. Carlyle Begay, elected as a Democrat, switched to the Republican Party.

Voters created the commission in 2000 to take on the politically charged job of drawing new maps every 10 years, instead of leaving it up to the Legislature.

This is the second high-court victory for the five-member commission.

Last year, in a 5-4 ruling, the Supreme Court rejected a challenge brought by legislative leaders that claimed only the state Legislature had the authority to draw congressional boundaries. Arizona lawmakers noted the U.S. Constitution gives state legislatures the power to set the “times, places and manner” of holding congressional elections.

The Associated Press contributed to this report.