On Monday night, Donald Trump's Commerce Department announced that, in response to a request from the Justice Department, it planned to restore a question about citizenship to the census questionnaire for the first time since 1950. This seemingly harmless move—which the Justice Department argued would make it easier to enforce the Voting Rights Act—sent shockwaves through the country. California promptly sued over the change and was soon followed by a bevy of other states like New York and Pennsylvania, and some Democratic politicians in Washington vowed to pass legislation preventing it.

With everything else going on under the Trump administration, the census might seem like a mundane matter. But a headcount of people—not just citizens—living in the US must occur every ten years by constitutional mandate. That count (the total number of "free persons") determines how many representatives in Congress each state gets, which in turn affects the electoral college and can generally reshape the political landscape for a decade or more. It also determines the allocation of federal resources and how state and local legislative seats are apportioned.

As a rule, the Census Bureau conducts a number of surveys, including a longform questionnaire that has asked some households about citizenship, status among other things. But the decennial census is the big one, and as former Census Bureau heads warned in a January letter, even small tweaks to the questionnaire can have potentially huge consequences. Indeed, even before the Commerce Department made its Monday announcement, some experts were fretting that the citizenship question being added to the census at large might scare off undocumented people and perhaps siphon more power to rural (GOP-friendly) locales.

To learn more, I called up Dowell Myers, a professor of policy, planning, and demography at the University of Southern California. He had some pretty dire things to say about this counting exercise and the future of our democracy.

VICE: What sorts of questions get asked during the course of a normal census?

Dowell Myers: The decennial census is supposed to be a 100-percent count of all the people in the United States. It doesn't have a lot of the details many of us would like to see, but there was a decision made with great consultation with Congress and the Office and Management and Budget over the last couple decades about what should be on the census questionnaire. The basic agreement is there should be as few questions as possible for fear of invading people's privacy and imposing "respondent burden." In other words, asking too many nosy questions will make people feel burdened by having to respond. They ask basic questions: How old are you? What is your sex? Is this house owned or rented? It's very short, and it has to fit on one page.

One problem with introducing a new question is it often forces an old question to get bumped off the survey. The real estate, as we call it, on the questionnaire is jealously guarded. We used to ask, for example, what kind of air conditioning do you have?

So what is the argument from the Trump administration about including the citizenship question?

I can't articulate their argument for them—you'd have to ask them—but the general argument, I think, is they can count people better if they know their citizenship status. But none of us who are experts in census-taking believe that's true. The more questions you ask, the worse the results will be. And if some questions create fear in the respondents, they won't respond at all. It's one of the reasons we don't ask about religion. We don't ask about political party.

Asking about citizenship is borderline—we do ask it on the longer questionnaire of a sample where we're not worried about getting a high percentage [of responses].

If the citizenship question were asked, that would mean a lot of undocumented people might refuse to answer any question and that population would be undercounted, right?

No. That's one argument someone might make, though.

So what are the consequences that could come from this question?

Any new question needs to be tested. [But] the testing period is closed, they're already done. That creates an enormous procedural problem here. It's a very formalized system, for accuracy. Number two, any new question will add to respondent burden—it will have a cost, no matter the question. Thirdly, anyone who does not like the concept of that question for whatever reason might decide not to respond. I'm told the Bureau has decided, if they include the question, it would come last on the questionnaire to minimize the effect of people throwing it away without responding.

I'm worried about rumors that will fly around about how this information will be used. You know there will be internet rumors. There is one precedent in the history of the United States that's very ugly and appalling: After Pearl Harbor, the Census Bureau was asked to provide the names and addresses of Japanese-American citizens—not just residents, _citizens—_and that was the basis of rounding them up for the internment camps. There is some suggestion that the administration might use that data in an aggressive manner as well. Just a rumor about that could really scare a lot of people who are citizens and might not want to be counted at all. It could snowball. It could really be bad.

Does the census normally share information with other government agencies?

It never shares any details about people's names and addresses. That's confidential, and always has been. But under the direction of the Justice Department, if they go extralegal, it might be able to be pried loose. It hasn't been pried loose since that incident with the 1940 census, and as a country we've come a long way since then.

But it is a concern of yours?

It's a new concern—not of mine, but new things have happened in the past year that have not happened before in the history of the country.

What do you think of the California lawsuit challenging this decision?

California is correct to raise the question—basically you take it to court to have the debate. Twenty-seven percent of California's population is foreign-born, by far the highest share in the nation, and in part that's how California's economy operates at such a high level of success. Immigrants are integral to that. The California attorney general is very much protecting their interests, which makes sense.

If the Democrats take back Congress in 2018, can they strike down this question through legislation?

I don't know the procedures. I do know that once the census is completed, you can't change it. It's there for posterity. The 2020 census, once conducted, will be used for all political apportionment until the 2030 census. Beforehand, if there was a change in the fall of 2018, I think it would raise havoc. The census has been put to bed. The questionnaires are set, it's been tested, you can't be making last-minute changes. You don't want to wing it. This is a very serious, solid enterprise, and you can't yo-yo back and forth.

If it were changed now, I don't know what would happen if the Democrats were to come to power—I don't know if they would change it back or not, because it's so difficult, and it creates such inaccuracies if you do change it.

It's not a casual enterprise, and I fear some elements in the Trump administration operate on a very casual basis, and that's not consistent with how the census operates.

This interview has been edited for length and clarity.

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