The Supreme Court may alter our democracy when it decides how to define districts in new case.

From a Brennan Center analysis by Michael Li and Eric Petry:

A big upheaval could be coming for America’s state legislatures. On December 8, the Supreme Court will hear oral argument in Evenwel v. Abbott, a closely watched case from Texas that will decide whether states must change the way they draw legislative districts. The new analysis in this paper shows that if the Evenwel challengers prevail, the nationwide impact will be far greater than previously assumed.

Like other states, Texas currently draws districts so they contain a roughly equal number of people rather than voters. Indeed, over the course of American history districts have overwhelmingly been drawn this way. But the Evenwel challengers say Texas’s legislative plans are unconstitutional because while districts may contain approximately the same number of people, many vary widely in the number of eligible voters.

So far, a lot of the attention around the case has focused on how changing the way districts are drawn would impact fast-growing Latino communities in certain states. And to be sure, some of the biggest changes would be in booming metro areas, such as Dallas, Houston, and Los Angeles, which have high numbers of both children and non-citizen immigrants. Latino majority districts, in particular, would become much harder to draw in many parts of the country.

But this new Brennan Center analysis shows the impact of a change would be far greater than expected and not confined to just a few states. In fact, if the Evenwel plaintiffs win and the rules are changed so lines must be drawn based on citizen voting age population instead of total population:

• Every state legislative map in the country would become presumptively unconstitutional under Equal Protection principles and would need to be redrawn.
• Nationwide, 21.3 percent of state house seats and 16.7 percent of state senate seats would be presumptively unconstitutional. In eight states, the percentage of house or senate districts with constitutional problems would be more than 40 percent.
• Redrawing maps to comply with constitutional requirements would require changing far more districts because of cascade effects from changes elsewhere on the map.

Read the full analysis here and below.