The history of the U.S. census asking about people's citizenship status is complicated.

Many of the stops and starts have been unearthed as part of the legal battle over the decision by Commerce Secretary Wilbur Ross, who oversees the Census Bureau, to add a citizenship question to the 2020 census.

At the Supreme Court last month, Solicitor General Noel Francisco argued on behalf of the Trump administration that a question about citizenship has "a long pedigree" as part of the national head count "in one form or another for nearly 200 years."

A close review of that history dating back to 1820, however, leads to one conclusion: Never before has the federal government used the census to directly ask for the citizenship status of every person living in every household in the United States.

"Secretary Ross's proposal to do just that is, therefore, historically unprecedented," write Thomas Wolf and Brianna Cea of the Brennan Center for Justice at the New York University School of Law, which has spoken out against including a citizenship question in the 2020 census.

Many in the news media, including NPR, have often referred to 1950 as the last time that the Census Bureau asked all households about U.S. citizenship status. A closer look at the 1950 census, however, shows that it wasn't a simple yes-or-no process.

In 1950, census workers asked about the birthplace of every member of each household. The question on the census worksheet was "What State (or foreign country)" was each person born in?

If the answer revealed someone had been born outside the U.S., census workers were instructed to "immediately" ask whether that person was naturalized, which would mean that the person had become a U.S. citizen.

The point of comparison to 1950, then, is that it's the last time the topic of citizenship was included in the census for all U.S. households.

Unlike how the census was conducted in 1950, the citizenship question that the Trump administration wants to ask next year is direct: "Is this person a citizen of the United States?" The 2020 question, if it is included on census forms, is intended to collect the citizenship status of every person living in each U.S. household, regardless of birthplace.

In the decades since 1950, the topic of citizenship has been part of census forms designed for some — but not all — households. Beginning in 1970, a sample of households encountered a citizenship question on what was known as the "long form" census.

After the 2000 census, the long form was replaced with an annual Census Bureau survey known as the American Community Survey, which provides the citizenship data that the federal government currently uses to enforce the Voting Rights Act.

The Trump administration has said it wants to collect citizenship data from all households through the 2020 census to help better enforce Voting Rights Act protections against discrimination of racial and language minorities. In recent decades, however, Census Bureau officials have recommended against using the census to ask all households about citizenship for fear that it would harm the accuracy of information collected for the head count.

The bureau's research indicates that a citizenship question is highly likely to scare households with noncitizens, including unauthorized immigrants, from participating in next year's constitutionally mandated count of every person living in the United States. The agency recommended to Ross that compiling existing government records on citizenship is a more accurate and less expensive alternative to adding a citizenship question.

Obtaining citizenship data about all U.S. households could have major implications for political representation at the state and local levels after 2020. Redistricting officials could use data on the citizenship status of every person living in every household to draw new voting districts made up of only U.S. citizens, rather than of all residents.

The Census Bureau's chief scientist recently confirmed that the bureau could make citizenship data available even if a citizenship question is not allowed on the 2020 census. The bureau could use the government records that Ross ordered the bureau to compile from other federal agencies in addition to adding a citizenship question.

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