The U.S. Supreme Court on Monday upheld the independent commission that draws Arizona's congressional map, ruling against the Arizona Legislature, which challenged the commission's authority by arguing the Constitution gave that power exclusively to lawmakers.
The high court, in a 5-4 decision, left in place a system created by voters in 2000 to encourage the creation of more-competitive congressional districts.
The independent commission is necessary to stop incumbents from gerrymandering districts to protect themselves and their political parties, advocates say.
But state lawmakers argued the U.S. Constitution gave them the power to draw congressional lines, not an appointed commission.
"This is a clear victory for the Arizona Independent Redistricting Commission and the Arizona voters," commission attorney Joe Kanefield said in a statement.
Commission chairwoman Colleen Mathis said she was 'thrilled" with the ruling and said it would ripple nationally.
"This is a victory not only for the people of Arizona, but for the entire country," she said in a statement.
GOP legislative leaders who brought the suit said they were disappointed by the ruling, adding that the court "has decided to depart from the clear language of the Constitution."
"It's unfortunate that the clear constitutional design has been demolished in Arizona by five lawyers at the high court," Senate President Andy Biggs, R-Gilbert, and House Speaker David Gowan, R-Sierra Vista, said in a statement.
Biggs said he was "highly disillusioned" with the decision, and speculated the ruling could have implications far beyond drawing political boundaries.
"This ruling seems to broaden the term 'Legislature'." Biggs said. And that could call into question any of the 90-member body's other actions, he said.
If the Republican-led Legislature had won, lawmakers might have drawn boundaries to favor the GOP. They could have lumped multiple incumbent Democrats into one district, such as U.S. Reps. Kyrsten Sinema and Ruben Gallego in Phoenix, or tilted to the right some swing seats, such as the northeastern Arizona seat currently held by Rep. Ann Kirkpatrick. She is running for the Democratic nomination for U.S. Senate, creating an open seat in that district.
Independent commissions across the country also could have been dismantled and political maps redrawn, in some cases in favor of Democrats, such as in California.
Dennis M. Burke was one of the authors of the 2000 ballot measure that created the commission.
"It was frivolous of the Republicans in the Legislature to challenge the law and take up the court's time with it," Burke said. "But the upside is it has shined a very bright light on a reform that other states will now take seriously."
Burke predicted the ruling would embolden other states to follow Arizona's model. California did so a decade ago, and activists from other states regularly contact him and others involved in the 2000 effort to learn what they can do in their states.
Election-law professor Jessica Levinson said she was surprised by the ruling after arguments in March appeared to favor the Legislature.
"I thought that they would give the constitutional provision a strict and narrow reading," said Levinson, of Loyola Law School. "I thought this was going to be another one of the cases where the court undermines voters rights and protections. This seems like it's a validation of citizens' ability to use their lawmaking power through the process of direct democracy."
Other lawsuits could still imperil the commission. It faces two other challenges to its 2011 work.
One suit, currently in Maricopa County Superior Court, challenges the congressional lines with different arguments. Action on that case has been on hold pending today's outcome. A third suit awaiting a decision by the U.S. Supreme Court disputes the legislative map, saying it was drawn to unfairly advantage Democrats. The court has not heard arguments in that case, but may take action when it issues a final batch of orders Tuesday.
The commission has prevailed in the cases thus far.