Professor Nathaniel Persily explains how the drawing of Congressional districts is addressed in the Constitution for The Associated Press.

Texas was the big winner in the 2010 census when it picked up four congressional seats, due mainly to growth in its Hispanic population.

A Supreme Court case being argued Tuesday threatens to diminish Latinos’ clout and benefit white, rural voters.

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The only reference to population and political districts in the Constitution requires the use of the once-a-decade census as the basis for divvying up congressional districts among the states, said Stanford University law professor and political scientist Nathaniel Persily. He said the challengers are arguing that the only population count prescribed by the Constitution should not be allowed to be used to draw political districts.

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But Persily said that while that survey has useful information, it is too imprecise for use in redistricting.