PHOENIX - Republican interests head to federal court today hoping to realign the state's legislative districts more to their liking.

Challengers are pinning their hopes on the fact that 30 districts crafted by the Independent Redistricting Commission are not all equal in population.

Attorney David Cantelme contends the differences were done "deliberately, intentionally and in violation of the one-person/one-vote principle."

The goal of the commission, he charges, was to cluster as many Republicans as possible together in districts, leaving the other, underpopulated districts with more Democrats than otherwise would occur, giving Democrats an unfair and illegal advantage in electing their own candidates to the Legislature.

Attorneys for the commission do not dispute the population disparities.

But Joseph Kanefield and Colin Campbell say any difference of less than 10 percent among the districts is "presumptively constitutional" unless challengers can prove there is an illegal or irrational basis for the differences.

They said the commission made changes to ensure compliance with the Voting Rights Act, which required creation of a certain number of districts where minorities have a chance to elect someone of their choosing.

Hanging in the balance could be the political makeup of the Legislature through the end of the decade. Before 2012, Republicans had 21 of the 30 Senate seats and a 40-20 edge in the House. Last year's election narrowed those leads to 17-13 and 36-24, respectively.

If the judges agree with challengers, they likely would order the commission to redraw the lines for the 2014 race, but this time with directions as to what they can and cannot do.

The panel consists of two commissioners chosen by top elected Democrats and two chosen by Republicans, with those four choosing a neutral fifth member. That person was Tucsonan Colleen Mathis, who is registered as a political independent.

Mathis never mentioned on her application that her husband, Christopher, worked on the campaign of a Democratic candidate for the Legislature in 2010, she donated money to the Democratic candidate for treasurer and her husband gave to Democratic causes.

"This consistent pattern of service to Democratic causes and patronage to Democratic candidates reveals that Chairperson Mathis is an independent in name only," Cantelme wrote.

Commission lawyers point out that Arizona, by virtue of historical discrimination, remains under a provision of the Voting Rights Act, which requires the state to get federal "pre-clearance" on any changes in election laws. That includes new district maps.

And, in general, that federal law precludes states from taking any action that would dilute minority voting strength.

One legal point that remains in dispute is who has to show what.

Cantelme contends it is up to the commission to show that every deviation from the ideal-size district was required to comply with the Voting Rights Act.

But Kanefield and Campbell say the commission's action is presumed valid, meaning the burden is on Cantelme to prove to the judges the changes were made "for illegitimate, arbitrary and discriminatory purposes."

Beyond that, they said the commission made population adjustments "to further other legitimate policies," including respecting communities of interest, using county boundaries when possible and creating as many politically competitive districts as possible.

Those goals are laid out in the 2000 voter-approved law that created the commission in the first place.

Before then, both congressional and legislative districts were drawn by lawmakers themselves, which allowed members of the dominant party to draw lines favorable to themselves and their political allies.