A sample census form is seen during the kickoff of...

A sample census form is seen during the kickoff of the 2010 Census Portrait of America Road Tour in Times Square in Manhattan on Jan. 4, 2010. Credit: Getty Images / Mario Tama

An essential moment arrives two years from April 1: Census Day 2020, the reference point for the big count of America’s whole population that happens every 10 years.

The count, however, might be flawed. With the late addition of a misguided question on citizenship, the census is in danger of being inaccurate. That matters to your wallet, ballot and health, among other areas of modern life touched by the census.

The census is sometimes described as the country’s largest peacetime mobilization. It counts everyone where they live in the United States. It’s required by the Constitution and was first held in 1790. The enumeration helped distinguish the new country from old nations. Many emperors and rulers have sent emissaries door to door to learn about their people — consider the story of Christmas and what brought Mary and Joseph to Bethlehem. But the American census was used to give the people power by determining voting representation.

Those high stakes, which extend from local to national office, are just part of the reason why the census is so consequential. Count wrong, and your vote might count less. The 2010 census reported 308.7 million people, and the 2020 count is expected to grow by more than 5 percent.

Then there is the money. Census data help determine the apportionment of hundreds of billions of dollars in federal funding every year. Businesses also rely on census information to know where to locate, hire and provide services. Cities use the figures to site hospitals and schools. The numbers contribute to an understanding of public health, too. All of the above rely on an accurate count of all people where they live.

That promise is under threat. First and foremost is the Trump administration’s irresponsible addition last week of a question about citizenship status.

There often have been partisan scraps over census practices, given the impact on elections. The concern this time is that in a climate of fear due to President Donald Trump’s increased immigration enforcement, noncitizens will be less likely to admit to their presence at an address. The fear recalls ugly moments in census history, such as when census data were used to help locate and confine Japanese-Americans during World War II. Today, privacy of census data is protected, but there are indications that many will still hide. Past census directors have sounded alarms, and census researchers last year wrote a memo about respondents’ fears. Censuses have often undercounted minorities, even apart from the sin of counting a slave as three-fifths of a person.

The citizenship question could have wide effects beyond undercounting — particularly in New York and on Long Island, which have significant non-citizen populations. The same fear of revealing personal data could scare off green card recipients, or prevent noncitizen parents from filling out forms for their citizen children. That affects all citizens, too, not just by upping costs as census takers search for non-respondents. An undercount of your neighbors wherever you are means less representation and funding for your community.

There is also little time to test this new question, a concern given that even smaller changes such as census instructions can have an effect on response rates. The citizenship question has not been asked of all respondents since 1950. It was included in the “long forms” sent to a small percentage of the population through 2000, not enough of a history to predict impact today. The main reason provided by Commerce Secretary Wilbur Ross in allowing the new question — that it will help enforce the Voting Rights Act — makes no sense because we already have data for that purpose from annual census operations.

There are other worries about the 2020 census. It has been woefully underfunded. Faced with a congressional demand after the last census to make the new one no more expensive, the bureau began counterproductive cost-saving as seen in the bureau citing cost concerns in the cancellation of crucial tests last year.

Through the chaos and austerity, the census bureau has been without a permanent director or deputy director since Director John H. Thompson left last year. Strong leadership is needed.

Finally, this census will embrace the internet era. In recent counts, census paperwork has been sent to households to be returned and counted, with census workers undertaking the laborious, expensive process of physically following up on non-returns. Now, you will be able to fill out the census questionnaire online. This is smartly modern. But in an era of hackable elections and malfunctioning software, cybersecurity is critical. This is just one more area in which more full testing is sorely needed, but at this point appears unlikely.

To save the census, the bureau must do what it can to pave over missteps so far. That includes coming up with more funding for outreach programs and advertising that can hopefully persuade people to do their civic duty. Certainly, people should respond to census queries. Most of all, Congress should pass a law to block the potentially disastrous citizenship question. Attorneys general around the nation are already filing lawsuits to do the same.

This is too important an issue to politicize. The count must be executed cleanly. After all, either way, for 10 long years, we’ll be stuck with the consequences.