The Trump administration announced late on Monday that it would be adding a question on citizenship status to the 2020 census.

It did so despite contrary advice from experts within the Census Bureau, civil rights advocates, social scientists and good-government groups across the nation.

There has not been a question about citizenship on the full-form decennial census since the 1950s. Any claims to the contrary — such as the ones White House press secretary Sarah Huckabee Sanders made on Tuesday — are false.

Commerce Secretary Wilbur Ross said the change was needed for accuracy. It comes in response to a December request from the Department of Justice, currently led by U.S. Attorney General Jeff Sessions.

Sessions, who is well known for a career spent in opposition to the expansion of voting rights for minorities, has claimed that a citizenship question will help prevent voting-rights violations.

It won’t, but that’s only part of the reason why the administration’s announcement was immediately met with lawsuits from multiple states.

California Attorney General Xavier Becerra filed a lawsuit on Monday night. New York Attorney General Eric Schneiderman announced on Tuesday that his state will lead a separate multistate lawsuit challenging the additional question. Other lawsuits, probably from voting-rights organizations, are sure to follow.

The best that can happen with a census that inquires into respondents’ citizenship status is that it undercounts the most vulnerable populations in this country, shortchanges diverse states on the funding they need to serve these populations and disproportionately shapes elections for the benefit of Republicans for the next decade.

Including a question on citizenship status will frighten noncitizens and immigrants, discouraging them from filling out the census forms and suppressing an accurate count of their population numbers.

The once-in-a-decade census numbers are widely used for matters of enormous national import. They’re the basis for everything from the determination of congressional districts to federal spending. Major cities and diverse states — including California — suffer the most when immigrants are under-counted in the census.

That’s the best-case scenario.

The worst-case scenario is that the Trump administration uses information about where noncitizens live in the U.S. to further its draconian priorities around deportation, or ill-conceived crackdowns on unproved accusations of “voter fraud.” These possibilities are too inhumane to contemplate.

There’s no good reason for a citizenship question on the 2020 census, but there are plenty of reasons not to have one. If the Trump administration doesn’t back down, California and other states should pursue their lawsuits until it does.

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