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A recent request by the Department of Justice to add a question on citizenship to the 2020 census could threaten participation, and as a consequence, affect the allocation of federal money and distribution of congressional seats.

In December, the Department of Justice sent a letter to the Census Bureau asking that it reinstate a question on citizenship to the 2020 census. “This data is critical to the Department’s enforcement of Section 2 of the Voting Rights Act and its important protections against racial discrimination in voting,” the department said in a letter. “To fully enforce those requirements, the Department needs a reliable calculation of the citizen voting-age population in localities where voting rights violations are alleged or suspected.” The request immediately met pushback from census experts, civil-rights advocates, and a handful of Democratic senators, who say that the argument is unfounded and that the timing of the request is irresponsible.

The census is used for allocating nearly $700 billion a year in federal money, electoral votes, as well as for the apportionment of House districts—that is, deciding how many representatives a state sends to Congress each year. The Census Act requires that all questions asked on the census fulfill a purpose. “If the Census Bureau or the administration can establish that there is a legal requirement, a requirement in law for citizenship data for the smallest levels of geography, then that would be justification for asking every household about the citizenship status of household members but no such law exists right now,” said Terri Ann Lowenthal, an independent consultant and leading expert on census issues. The bureau is then required to submit a final list of questions, which are tested beforehand, for the decennial census two years before its roll out. The bureau needs to send the questions for the 2020 census to Congress by April, leaving the bureau little opportunity to test a new question before submitting it to Congress.

Congressional apportionment is based on overall population, not citizens, specifically, therefore an inaccurate count would directly affect how seats in the U.S. House are distributed. That means that if fewer undocumented immigrants or minorities are willing to participate in the census, it could affect the political balance in Congress, since those populations tend to be concentrated in cities, where Democrats draw most of their support. According to a study by Election Data Services Inc., based on population estimates by the Census Bureau, up to 16 states could either lose or gain a congressional seat as a result of the decennial census. Minnesota, for example, is at risk of losing a seat in the House and is relying on an accurate census count to keep it.

Some Republicans and anti-immigration groups see the undocumented population as conferring an unfair advantage on Democrats.

“If 50 percent of the illegal alien population resides in California and we’re not differentiating them in the census and we’re basing apportionment in the census on those figures, then some states are losing representation while others are overrepresented,” said Chris Chmielenski, the director of content and activism at NumbersUSA, which supports reduced immigration. Republican Representative Steve King of Iowa, an ardent opponent of immigration in the House, expressed support for the DOJ’s request, arguing that it would benefit his state: “In districts like Maxine Waters, who only needs about 40,000 votes to get reelected in her district and it takes me over 120,000 in mine because hers is loaded with illegals and mine only has a few.”

The Justice Department says that asking the entire U.S. population about their citizenship status is necessary for the enforcement of the Voting Rights Act, which prohibits racial discrimination at the polls. The last time the entire U.S. population was asked about citizenship status was in 1950, 15 years before the law’s passage. Since then, the question has been included in the American Community Survey, which is sent out every year to a sample of the population; census experts say that’s enough to enforce the Voting Rights Act.

“I think the argument ridiculous. The Justice Department has never needed or asked for that question on the short form of the census before and the enforcement of the Voting Rights Act does not need it,” said Vanita Gupta, the president and CEO of the Leadership Conference on Civil and Human Rights who ran DOJ’s Civil Rights Division under Obama, referring to the form that is sent to every household. Census experts and civil-rights advocates argue that there’s no justification for asking everyone in the United States about their citizenship status and that doing so could have a crippling effect on participation.

The Census Bureau said in a statement that it’s “evaluating the request from the U.S. Department of Justice and will process it in the same way we have historically dealt with such requests.” It continued: “The final list of questions must be submitted to Congress by March 31, 2018. Secretary Ross will then make a decision. Our top priority is a complete and accurate 2020 census.”

Questions on the census, the first of which took place in 1790, have changed over the years depending on what was most relevant to the time period. In the mid-19th century, for example, the census began asking respondents where they were born to track internal migration. “Why questions go off and on the census often has to do with competing interests,” said Margo Anderson, a professor of history and urban studies at the University of Wisconsin-Milwaukee and author of The American Census: A Social History. She added that after the passage of the Immigration and Nationality Act of 1965, which dramatically changed U.S. immigration policy by ending a quota system based on national origin, the census reinstated a question on citizenship but only to a sample of respondents.

Statisticians over the years had been learning new ways to collect data, particularly in sample sizes, allowing the bureau to pose questions to a segment of the population and therefore lessen the burden on people while still gathering useful data. There was no longer a need then to ask everyone about their citizenship, which is considered an identifier and not a characteristic that would be used for statistical analysis; it could instead be asked to only some respondents. The “long-form” census, which included more questions and was only sent out to some respondents every 10 years, included a question on citizenship. Those answers quickly became dated, so the bureau introduced the American Community Survey, which would ask questions included in the “long-form” but do so every year. That continues to be the case today, fueling arguments against the DOJ’s request to reinstate it in the general census.

Civil-rights and immigrant advocates worry that changes to the census will stunt the progress made in recent years to increase participation among minorities. Arturo Vargas, a member of the National Advisory Committee on Racial, Ethnic, and Other Populations, and the executive director of NALEO Educational Fund, a Latino advocacy group, noted that historically, the biggest challenge for the Census Bureau has been overcoming people’s distrust.

“People are scared of how the federal government is enforcing immigration laws,” Vargas said. “If a citizenship question is added to the decennial census, then this fear people have is going to result in less people wanting to respond to the census, which will produce a very inaccurate census and will actually increase the Census Bureau’s cost and budget to conduct the census.” In cases where the Census Bureau doesn’t receive a response, it has to send enumerators to the address to interview those who haven’t responded—an expensive process.

Respondents’ recent reactions have led the bureau to believe this may be an issue in the 2020 census. Last year, field representatives found that respondents “intentionally provided incomplete or incorrect information about household members” and “seemed visibly nervous.” In one Spanish interview, the respondent said, “The possibility that the Census could give my information to internal security and immigration could come and arrest me for not having documents terrifies me.”

In fact, by law, the Census Bureau cannot provide personal information of any kind to a government agency. But that doesn’t keep people from worrying about it, particularly those who may be undocumented or have mixed-status families. In the past, people unable to distinguish between immigration officers and government workers have been afraid of raids as officials went door-to-door asking for information, said Eric Rodriguez, the vice president of UnidosUS’s Office of Research, Advocacy, and Legislation.

The federal government has tried to remedy these concerns. In 2000, U.S. Immigration and Naturalization issued a moratorium on highly visible enforcement so as not to interfere with the census. “It is crucial that undocumented as well as documented aliens understand that they are expected to respond to census-takers and questionnaires, and that there is no nexus between the census and INS enforcement activities,” Michael A. Pearson, an executive assistant commissioner at the INS, wrote in a memo at the time.

Concerns shared about how some communities might react to the census therefore are not new, but they are worsened by this administration’s crackdown on immigration.

This puts Latino advocacy groups in a bind: They need to encourage people to participate and raise awareness about the census, but they’re doing so under an administration that has consistently used harsh rhetoric against immigrants and rolled out policies aimed at casting a wider net on those eligible for deportation.

Rodriguez said that what the government does in the coming years will have an effect on how respondents behave. “Quite honestly, it’s just making sure that the government doesn’t do things to create less trust in the census itself and doesn’t do things to undermine the integrity of the Census Bureau in the process and that does have to do with information sharing agreements between agencies, what Homeland Security might in fact be doing over the next few years around deporations and enforcement and usage of government information,” Rodriguez said. “All of those things could in fact substantively call into question what the government is doing and so, there’s work that has to be done to in fact make sure that the government is obviously abiding to the law but not doing things that are detrimental to communities for whom we need a great and effective count in 2020.”

Rodriguez likened the situation to the Deferred Action for Childhood Arrivals program, which Trump ended last year: Advocates encouraged people to sign up to the program, which shields immigrants brought to the U.S. as minors from deportation, but years later, those recipients are in limbo, as a result of the program’s termination. “We have to go on the information that you have at the time, and for many, coming out of the shadows is an important opportunity,” he said.

The prospect of asking millions of people what their citizenship status is enough to stir concern among observers and alienate minorities already worried about the information provided on the questionnaire.

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