Here are some of the possible court rulings, as well as what they mean for Congress.
Scenario 1: Status quo. Arizona's map would remain unchanged if the court rules in favor of the commission. In that case, Republicans will still have four safe districts, Democrats will have two safe districts, and three will be toss-ups. And rather than allowing the legislature to draw lines without many regulations, it would continue to require that the commission create as many competitive districts as possible in future redistricting sessions.
That doesn't help Tobin's chances at Congress in 2016, but he would still have a reasonable chance. He lost to Democratic incumbent Ann Kirkpatrick by just 5 percentage points last cycle, and the district still leans Republican—and against President Obama.
This scenario would be the most favorable for Democrats, who would have a reasonable chance at holding five of the state's nine seats—which they did from 2012 to 2014—if they overperform and win all three swing seats. By not pushing any more Republicans into swing districts, it would give Democratic Rep. Kyrsten Sinema a likely path to reelection if she chooses not to run for Senate and would keep Republican Rep. Martha McSally on her toes.
Scenario 2: SCOTUS tosses out Arizona's system and the dominoes fall. The Supreme Court could rule that a truly independent commission like Arizona's—one that draws maps without running them past the legislatures—is unconstitutional because they cut the elected lawmakers out of the redistricting process. In that case, the Arizona legislature will redraw the map from scratch. And it's likely they'll be required to do that immediately, rather than waiting until the next redistricting year after the 2020 Census, said Justin Levitt, a professor at Loyola Law School who filed an amicus brief siding with the commission.
Tobin, who railed against the current maps while serving as speaker of the state House, said that in drawing the lines, his party wouldn't gerrymander any more than the commission did. For evidence, he points to the state's two rural districts that loop oddly around different regions. The district he ran in, for example, covers a portion of northwest Arizona, the entire northeastern portion, an area just north of Tucson in the southeast, and a small part of the southern Phoenix metro area in the center of the state.
From Democrats' perspective, this ruling would guarantee a negative outcome, because Republicans would be in charge of drawing the maps. "It's going to be bad for Democrats and bad for Arizona," said D.J. Quinlan, executive director of the state Democratic Party.
Quinlan said he would expect Republicans to try to draw six safe Republican districts instead of the current four, one "semi-competitive" district that would lean Republican, and two Democratic districts that pack as many liberal voters into Reps. Raul Grijalva's and Ruben Gallego's districts as possible.