The U.S. Supreme Court heard arguments this week in United States Dept. of Commerce v. New York, a case that will determine if the Census Bureau can reintroduce a citizenship question on the 2020 decennial census. While adding a citizenship status question may seem a reasonable public policy decision — virtually every country in Europe and elsewhere does so — it has generated a heated political debate about reapportionment, redistricting, federal funding, and, naturally, partisan power.

Let’s hope the justices allow a citizenship question, because it has the potential to restore electoral equality for all U.S. citizens as well as the principle of one person, one vote.

The case pits the State of New York and an alliance of blue states against the U.S. Department of Commerce, the agency that oversees the decennial U.S. census. The plaintiffs allege that reintroducing this question on the form that goes to all households will result in a dramatic undercount of noncitizens, on the theory that response rates from fearful Hispanics will plummet. This question, they claim, will result in the loss of their targeted federal funds and, for the states, electoral votes and seats in Congress.

The Trump administration wants the question reintroduced — it was asked of every household until 1950 — in order for the Justice Department to more effectively enforce Section 2 of the Voting Rights Act, the provision that protects minority electoral opportunities. DOJ asserts that its lawyers need to have geographically detailed household information that includes citizenship status as well as other data such race and ethnicity. Currently, the only source of citizenship data is an annual estimate conducted by the Census Bureau’s American Community Survey.

Late last year, a federal court in New York ruled that adding the citizenship question would create “a veritable smorgasbord of classic, clear-cut" violations of the Administrative Procedure Act. New York argued that the decision to add the citizenship question was “arbitrary and capricious” and thus, a violation of the APA.

For states such as New York with significant percentages of non-citizens, a population undercount could threaten their share of the nearly $900 billion in annual federal funding. Moreover, New York asserts that an undercount may affect the number of congressional districts it will be apportioned in 2021.

California and New Jersey, as well as dozens of left-leaning advocacy groups, have rushed to support New York in its effort to eliminate the citizenship question. What’s bewildering about these Democratic-leaning states’ claims is that Republican-leaning states such as Texas and Florida, which also have large noncitizen populations, are defending the reintroduction of the citizenship question.

If California and New York are worried about the consequences of a population undercount, why aren’t Texas and Florida?

So, who is right? The blue states or red states? Or is there another explanation for the split?

What may be motivating Republican-leaning states to support the citizenship question is how redistricting will be conducted in 2022, the year that virtually every voting district in the nation will be redrawn. Having total population and citizenship data would create an important governance option for many states and localities.

Specifically, once states and jurisdictions have citizenship data by geographic census blocks (there are over 11 million uniquely numbered ones), those with large percentages of noncitizens may choose to draw new voting districts that equalize the total number of citizens in each district instead of the total number of persons.

For decades, states have been compelled to equalize the total number of persons for each voting district in order to comply with the constitutional doctrine of “one-person, one-vote.” However, a 2016 Supreme Court case, Evenwel v. Abbott, expanded their options to include equalizing for total population or citizen population.

Equalizing for citizen population, rather than total population, will have the effect of giving eligible voters equality of electoral power.

Consider this: In states with large numbers of noncitizens such as Texas, New York, and California, some state legislative districts may have twice as many eligible voters as adjoining ones. This means districts with fewer citizens have more electoral power than the districts with more citizens.

That isn’t fair. Equalizing districts by the number of citizens prevents some voters from having their votes over-weighted and over-valued, while others are under-weighted and under-valued. If one-person, one-vote — one of our most enduring egalitarian principles — has any meaning, the citizen population gaps in voting districts must not be so glaringly wide.

Without census data that includes citizenship status, it is probably not possible for states and smaller jurisdictions to draw election districts that equalize eligible voters.

Let’s hope the justices see it that way.

Edward Blum, a visiting fellow at the American Enterprise Institute, is the president of the Project on Fair Representation.