liveslow/iStock(WASHINGTON) — Earlier this month, a chilling missive arrived at the Chicago office of the American Civil Liberties Union: a fake ACLU flier that had surfaced online, calling on immigrants to boycott the 2020 census.

“If you get a census form, do not fill it out! ICE will find you and deport you!” it warned. The document went on to advise people to destroy any census form that arrives in the mail and to ignore knocks at the door from census workers. “Federal Department of Commerce agents will be looking for any evidence of identity theft, outstanding warrants, and anyone subject to deportation orders. Remain Silent. Protect your Information.”

“This isn’t really you guys, is it?” wondered the concerned tipster, who first alerted Ed Yohnka, the ACLU’s communication’s director in Chicago, to the ruse.

The flier was a hoax, but it was “concerning and alarming” all the same, Yohnka said.

For months, the ACLU has been fighting the Trump administration’s efforts to add a citizenship question to the once-per-decade population count because they believe it would discourage non-citizens from participating. On Thursday, Trump acknowledged that time had run out and said his administration would drop the effort to add the question, while pushing ahead with an attempt to count U.S. citizens by other means.

While that might be viewed as a victory, lawyers and immigration rights advocates who opposed adding the question told ABC News that, like a bell than can’t be unrung, the mere discussion of it, coupled with the president’s Muslim ban and policies on immigrants at the southern border, has left people on edge.

The census, which is often described as the nation’s largest peacetime mobilization, forms the basis for all the government’s population data and is the basis for deciding congressional apportionment, as well as how much federal money should go to senior centers, schools and sidewalks.

Worry about whether information could be passed on to immigration authorities features prominently at information sessions about the census, the National Association of Latino Elected Officials and other groups have said. There is also mounting concern that hoaxes like the ACLU flier will appear on social media to discourage people from being counted — a concern that is all the more acute because 2020 will also mark the first time that a U.S. census is conducted largely online.

“At every forum I go to, the minute I bring this up, there is a plethora of questions,” said Anita Banerji, who is leading census 2020 outreach in Illinois for the non-profit group Forefront, which partners with the ACLU. “Whether the question is on the form or not, the damage has been done,” she said.

It is illegal for information obtained by the census to be used for any other purpose, and the Census Bureau goes to enormous lengths to shield its data from hackers. Still, that fear is not without precedent. During World War II, Japanese-Americans were rounded up in part thanks to census data.

“You have a federal surveying process being done by a federal government that’s been based on one of the deepest levels of xenophobia and anti-immigrant sentiment in the history of our country. Even without the citizenship question, this was always going to be complex,” said Betsy Plum, the vice president of policy at the New York Immigration Coalition, an immigrant rights group.

Dale Ho, Director of the ACLU’s Voting Rights Project and one of the lead attorneys in the federal case in New York that challenged the addition of the citizenship question, said that while there is anecdotal evidence that non-citizens are fearful of participating in the census — with or without the citizenship question — the ACLU is doing everything it can to encourage participation.

“If they added this question because they want to dilute the clout of immigrant communities and communities of color, then not participating in the census is letting them win,” said Ho.

Immigrant rights groups argued the effort was a purely partisan attempt to unfairly reduce the electoral power of areas with large numbers of immigrants — likely benefiting Trump and the Republican Party — and could jeopardize billions of dollars in federal funding to municipalities across the nation.

Those who support adding the question note that the count is required by the Constitution and they say the government has every right to count its citizens.

“When is it a bad idea in a democracy to get more data?” said David Rivkin Jr, a lawyer at the Washington firm BakerHostetler, who served in various legal positions throughout the Reagan and George H.W. Bush administrations.

For the most part, opponents of adding the citizenship question have prevailed.

Last month, the Supreme Court issued a mixed opinion, ruling that the administration, while potentially in its rights to add a census question, would need to offer a more compelling rationale before dong so.

The administration appeared at first to accept defeat, announcing that the planned printing of the census had begun and that the citizenship question would not be included. But then, the president reversed course, saying in a series of tweets that the fight over adding the question was not over.

Conducting the decennial census is a complicated process. After the initial self-response period, census workers visit the homes of people — often multiple times — who did not respond or gave partial responses.

But census bureau officials themselves concede that despite the effort, it’s an imperfect science: whites — who are more likely to own multiple homes and have grown children counted at multiple addresses — are over-represented, while other populations are under-counted.

The decennial census has not asked directly about citizenship since 1950, though the question has been included in the so-called “long-form” survey, which goes to a sample of U.S. households every year and is now known as the American Community Survey.

No one can say definitively how a citizenship question would have impacted response rates since the exhaustive, years-long testing that typically precedes any change to the census was not done in this case because the decision to add it came too late. During the trial in New York federal court last year, John Abowd, the census bureau’s chief scientist, said that he expected a drop in self-responses, especially among Latinos, but said he believed the bureau could make up for the gap in its follow-up process.

A June report from the Census Bureau’s Center for Economic Studies found that including the question would precipitate an 8 percent drop in self-responses in households with at least one non-citizen. Given that approximately 28 percent of households potentially have at least one non-citizen, that potentially means a 2.2 percent drop in self-responses overall “increasing costs and reducing the quality of the population count.”

Documents made public in May revealed that Republican strategist Thomas Hofeller (nicknamed the “Michelangelo of gerrymandering” for his role in Republican redistricting) concluded in 2015 that adding the question could be a huge boon to Republicans when they redraw Congressional district maps, and suggested a rationale that Commerce Secretary Wilbur Ross would later offer publicly: that it was a necessary addition to help enforce the 1965 Voting Rights Act (VRA). The documents were discovered after Hofeller’s death.

In his majority opinion, Chief Justice John Roberts agreed with Ross that there was “limited empirical evidence” on what the impact on turnout would be.

“Weighing that uncertainty against the value of obtaining more complete and accurate citizenship data, he determined that reinstating a citizenship question was worth the risk of a potentially lower response rate,” Roberts wrote.

People on both sides of the debate meanwhile say that the citizenship question debate has distracted attention away from another pressing matter: this is the first year that most questionnaires will be filled out online.

Greta Byrum, the co-director of the Digital Equity Laboratory at The New School in New York, said that since home Internet access is more prevalent in wealthier and white households, the digital census could lead to an under-count of less wealthy and non-white households — a problem that is only exacerbated by the relatively little public outreach thus far about the census’ digitization.

“Hard-to-count populations are also on the wrong side of the digital divide,” Byrum said. “And it’s not going to improve response rates if people are surprised by this.”

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