For 50 years the "one person, one vote" principle has been used to divvy up political power by counting all people in states and putting them into electoral districts of roughly equal size.
But the mathematics of power may be about to change in a way that could shift political clout away from fast-growing Latino communities in states such as California, Texas and Florida and move it to the suburbs and rural areas.
The Supreme Court surprised election-law experts Tuesday and said it would hear arguments this fall about whether voting districts should continue to be drawn by using census population data, which include noncitizen immigrants who are in the United States both legally and illegally, or whether the system should be changed to count only citizens who are eligible to vote, as conservative challengers are seeking.
In California and other states with large noncitizen populations, a switch in who gets counted could have a huge effect.
Districts in the Legislature are required to have virtually the same population. But in some districts, a large share of residents are noncitizens. That's particularly true in parts of Los Angeles and the Central Valley that have large immigrant populations. The number of citizens can be as much as 40% higher in some districts than in others.
For example, when the state did its last redistricting after the 2010 census, the 23rd state Senate District, which covers Rancho Cucamonga and neighboring towns, had one of the smallest shares of noncitizens among its population. By contrast, the 24th District, covering the Eastside of Los Angeles and represented by Senate President Pro Tem Kevin de Leon, had the largest share of noncitizens.
Currently, voters in each of those two districts get to elect one state senator. But if the court were to say that districts must have an equal number of citizens, rather than an equal number of people, the Eastside district would be much too small and would have to be combined with other parts of Los Angeles to make up a full district. Its voters would lose political power. Conversely, voters in the Rancho Cucamonga district would gain clout.
Across the state, such a readjustment would shift power away from immigrant-heavy places, which tend to be poor. Areas that would gain power would primarily be wealthy regions where noncitizens generally cannot afford to live.
"If the Supreme Court acted on it, it would devastate Latinos and Asians and the districts currently held by Latinos, Asians and African Americans in California," said Alan Clayton, a redistricting consultant who advises Latino elected officials. "It would decrease the power of Latinos and Asians in the Assembly, Senate and Congress."
In addition to the Rancho Cucamonga district, the state Senate districts with the lowest share of noncitizens include the 26th, centered on Santa Monica and Malibu, the 11th in San Francisco and the 1st and 2nd in the far northern reaches of the state, according to data from the state's nonpartisan citizens redistricting commission.
A similar switch would take place on the local level. Within Los Angeles County, for example, power on the Board of Supervisors probably would flow from the immigrant-heavy Eastside and South L.A. to the affluent Westside and western San Fernando Valley.
At City Hall, "you'd probably go to two members on the City Council representing South L.A." rather than the current three, said Andrew Westall, who ran the city commission that last redrew the city districts in 2011. "It would decrease the influence of that part of the city. You'd probably end up with less minorities on the City Council, whether African American or Latino."
How such a switch might affect the partisan balance within the state is harder to forecast, in part because much depends on how new district lines might be drawn. Currently, Democrats represent many of the areas that would be relative losers, but also many of the affluent districts that would gain clout.
But Assemblyman Luis Alejo (D-Watsonville), chairman of the Latino Legislative Caucus, said the issue was a question of fairness.
"Many of us who represent a large number of noncitizen immigrants assume a responsibility to represent everyone within our districts, regardless of their citizenship status," he said in an email. "These individuals deserve to have representatives that will also champion their concerns too."
Despite decades of rulings on voting rights, the issue of who gets counted is one the justices have never clarified. As far back as 2001, Justice Clarence Thomas said the court should consider counting voters, rather than the total population, when dividing up districts. But until Tuesday, the other justices had not shown an interest in joining with him on the issue.
The Texas case was brought to the high court by Edward Blum, a conservative activist who two years ago won the Supreme Court ruling that struck down part of the Voting Rights Act. Blum also launched a constitutional challenge to the affirmative action policy at the University of Texas that is still pending.
"My interest is in restoring the original principles of the civil rights movement of the 1960s," Blum said Tuesday.
He has tried for more than 15 years to persuade the high court to clarify the "one person, one vote" rule. "I'm hopeful and confident we will prevail," he said.
Blum sued on behalf of Sue Evenwel, a county chairwoman for the Texas Republican Party who lives in mostly rural Titus County in east Texas. She sued claiming her right to an equal vote is being undercut because the district where she lives had 533,010 citizens of voting age in 2011, while another Senate district had far fewer, only 372,000 citizens of voting age.
A three-judge panel rejected her claim and said Texas and other states were free to rely on census data for drawing districts. Those judges said her appeal rested "upon a theory never before accepted by the Supreme Court or any circuit court" that only voters should be counted in drawing districts.
In her Supreme Court appeal of Evenwel vs. Abbott, her lawyers argued that requiring states to switch to counting only citizens would "ensure that voters are afforded the basic right to an equal vote."
The Supreme Court adopted the "one person, one vote" rule in 1964 in Reynolds vs. Sims. Though the case came from Alabama, many states had legislatures that favored rural interests. In California at the time, Los Angeles County, with 6 million people, had one state senator, the same number as the smallest rural county with only 14,000 people.
"Legislators represent people, not trees or acres," wrote Chief Justice Earl Warren. "As long as ours is a representative form of government," it is not fair or equal, he said, to permit some votes to count for far more than others.
The rule, based on the equal protection clause of the 14th Amendment, is applied to all state elections, including for state legislators, county boards, city council or local school boards.
The appeal the justices agreed to hear does not directly challenge congressional districts, but if the justices rule broadly, they could affect those districts as well.
At least once a decade, voting districts may be redrawn based on new census data. Though census data is considered reliable, Stanford University law professor Nate Persily, an expert on voting, questioned whether comparable figures exist to tally the number of eligible voters.
"We don't have a national list of citizens," he said. The data cited in the Texas case come from a census survey of about 2% of households that counts citizens.
"If you are only counting 2% of the households, there will be wild inaccuracies. It would be crazy to force states to draw districts with this data," he said.
The appeal in the Texas case noted that same issue arose in Los Angeles County in 1990. By a 2-1 vote, the U.S. 9th Circuit Court of Appeals upheld a ruling that required the Board of Supervisors to redraw its districts and create one with a Latino majority. In dissent, Judge Alex Kozinski questioned the premise of relying on the total population figures, rather than on the count of citizens who were eligible to vote.