Washington (CNN)A battle has been brewing over the 2020 Census: Should every member of the US population be asked about citizenship status?
Both sides say their position will produce a more accurate accounting of the population. Critics say asking about citizenship could scare minorities from responding and leave them uncounted. Supporters say a better understanding of where the citizenry lives will improve elections.
The decennial census count is used to divide up congressional seats and apportion millions of dollars of federal funding.
The debate heads to the Supreme Court on Tuesday for oral arguments. The high court picks up the case after three lower courts issued stinging rulings striking down the question.
How and why was citizenship added to the Census?
In March 2018, Commerce Secretary Wilbur Ross announced the 2020 Census would ask the entire US population about citizenship status -- a question not posed on the survey sent to every household since 1950.
More recently the question has appeared on surveys sent to a sample of the population, such as the American Community Survey and the so-called long form survey.
The process formally began with a request from the Justice Department in December 2017 "that the Census Bureau reinstate on the 2020 Census questionnaire a question regarding citizenship." The resulting data is "critical" to understanding the localized population of eligible voters so it can enforce the Voting Rights Act and prevent racial discrimination at the polls, DOJ said.
The career leadership of the Census Bureau urged Ross to find a different solution. They wrote adding the question "is very costly, harms the quality of the Census count" and would produce less accurate data than the government could compile by analyzing data collected in other ways.
But Ross wrote that asking the question "of 100% of the population gives each respondent the opportunity to provide an answer," and the non-responsive holes can be filled through the other data, known as "administrative records."
Why is it controversial?
Critics accuse Ross of concealing the true origins of the change, and question his motivations.
They note that the DOJ letter came after Ross reached out to Attorney General Jeff Sessions, and that months before, White House strategist Steve Bannon had connected Ross with Kris Kobach, who led a much-criticized panel investigating alleged election fraud.
In one email, Kobach wrote to Ross that the lack of a citizenship question means, among other consequences, "aliens who do not actually 'reside' in the United States are still counted for congressional apportionment purposes."
And two months before that, Ross questioned an aide by email: "I am mystified why nothing have been done in response to my months old request that we include the citizenship question. Why not?"
Ross later testified before Congress the decision did not involve the White House.
"Has the President or anyone in the White House discussed with you or anyone on your team about adding this citizenship question?" Rep. Grace Meng, a California Democrat, asked at a hearing in March 2018. Ross replied: "I'm not aware of any such."
In March 2019, Ross told Congress that he had misunderstood her question and "testified truthfully to the best of my ability in response to what my understanding of what the questions were."
Administration attorneys have argued in court that Ross' motivations are largely insignificant, as long as he ultimately provided a good reason for making the decision.
What have the courts said so far?
Three federal trial courts have issued a series of stinging opinions finding constitutional and legal violations in the question itself and the process for developing it.
Most recently, a federal judge in Maryland said the scientific data presented at trial "confirms that the addition of the citizenship question will result in less accurate and less complete citizenship." Asking the question would violate the Constitution and "unreasonably compromise" accuracy of the census, the ruling read.
That ruling followed two similar rulings from courts in New York and California, which the government appealed to the Supreme Court.
What happens after the Supreme Court rules?
The Census Bureau says it is ready for whichever decision the high court hands down. It has prepared two versions of the paper and electronic survey.
Officials are also currently conducting a field test of the question to determine how to best get out their messages: That the data matters, and that federal law prevents the Census Bureau from sharing names or answers with immigration enforcement.
They say they have the resources to conduct follow-up mailings and visits with households who do not respond and say the penalty for not responding to the census has not been enforced.
Government attorneys told the courts they need a decision by the end of June. The printing presses for response forms, the Census Bureau says, are scheduled to start running on July 1.
