The U.S. Constitution says that "We the People" are the source of political authority in America. But just who are "the people"? That's a big and basic political question, and today the Supreme Court gave its answer — in a unanimous decision.

The court ruled that the total population as defined by the Census Bureau should be used when counting people for political purposes. That means all persons residing in a particular state or district are to be counted, not just those who are eligible to vote.

The challenge came from Texas, though that state counts its population for political purposes the same way the other 49 states do. It was brought by the conservative activist group Project on Fair Representation, which in recent years has pursued successful legal challenges to parts of the 1965 Voting Rights Act and the affirmative action policies of the University of Texas, Austin.

The challengers had argued that only citizens who are at least 18 years old should count when separating the population into voting districts (which are drawn to have about the same number of people).

They said eligible voters have a disproportionate impact in voting when they live in districts with large numbers of ineligible people (noncitizens and nonadults). Conversely, they argued, those living in districts with fewer ineligible people had their voting power diluted.

The plaintiffs said this violated the constitutional principle of equal protection under the law.

The situation they were describing is mostly likely to occur in states with large numbers of immigrant residents, such as Texas, California, Florida, New Jersey, Arizona and Nevada. It would also affect large cities with sizable immigrant populations.

The practical effect would be to create more legislative districts where older and enfranchised people are predominant, and fewer districts with large populations of people ineligible to vote.

The decision, written by Justice Ruth Bader Ginsburg, based its reasoning in the federal practice of defining population as all persons. Five justices joined with Ginsburg in her opinion. Two others, Justices Clarence Thomas and Samuel Alito, wrote their own concurring opinions. They agreed that Texas could not be forced to change its method of counting, but they maintained that any state could do so if it chose.

Supporters of the total population standard hailed the court's decision, saying the opposite outcome would have been an earthquake — forcing a massive revision of districts in many states. Experts said such revision would have increased the legislative and political clout of rural and exurban areas (which typically vote Republican) at the expense of city residents – many of them minorities and recent immigrants (who typically vote for Democrats).

Voting expert Nathan Persily has drawn legislative maps for states and local jurisdictions across the country. He said this was the intent of the challengers.

"A ruling in their favor not only would have led to a diminishing of Latino representation in Texas, but it would have forced many jurisdictions throughout the country, maybe hundreds, to redraw their lines."

Writing for the court, Justice Ginsburg noted that the Constitution's framers made each state's total population the basis for allocating seats in the U.S. House of Representatives. That, she said, ensured that all people — not just voters — count in our system of government accountability.

She added that in enacting the 14th Amendment, Congress reaffirmed the idea of representational equality by explicitly rejecting a proposal for apportionment based on voter population instead of total population. It cannot be, she said, that the 14th Amendment mandates counting all residents, then turns around and forbids states to use that same system to draw their own legislative district lines.

Edward Blum, president of the Project on Fair Representation, the group that brought today's case, said the court had still not ruled out letting states choose between total population and eligible voters.

"Perhaps," said Blum, "another lawsuit after the next round of redistricting will compel the court to clarify once and for all where it stands."

But voting specialist Richard Hasen at the University of California at Irvine notes that today's ruling makes the current system a safe harbor and states are likely to stick with total population.

"If you try to do something else," said Hasen, "then you run the serious risk of litigation."

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