WASHINGTON — The Supreme Court’s ideological divide was on full display Tuesday, and it seemed from their questioning that the court’s conservatives were likely to defer to the Trump administration on adding a question concerning citizenship to the 2020 census form sent to every American household.
The court’s liberal justices were skeptical of the case offered by Solicitor General Noel Francisco, who represented the administration. They peppered him with questions, and the exchanges between Francisco and Justice Sonia Sotomayor at times seemed tense.
She frequently cut in to debate him, setting the stage for an animated, sometimes technical discussion over the administration’s objective and the impact it could have.
The outcome will be significant, given that the census ultimately helps determine congressional representation, how the federal government allots billions of dollars in funding, and more. The census hasn’t asked a citizenship question of each household since 1950, and three federal district court judges have forbidden the Commerce Department from adding it to the upcoming count.
‘‘Enumeration is how many people reside here,’’ Sotomayor said. ‘‘Not how many are citizens.’’
At the heart of the debate was Commerce Secretary Wilbur Ross’s decision to add the question and what the Trump administration would do with the results.
‘‘There’s no doubt that people will respond less,’’ Sotomayor said at one point. ‘‘If you’re talking about prediction, this is about 100 percent that people will answer less.’’
Francisco said that Ross ‘‘understood there was a downside’’ to asking the citizenship question but also that the secretary felt there was more to gain from adding it.
‘‘He concluded that the benefits outweighed the costs,’’ Francisco said.
The discussion frequently diverted into technical discussions of predictive studies and error rates, but it returned repeatedly to an issue that has lingered over the case: Ross’s rationale for adding the question.
The federal judges who previously weighed in said that his explanation was pretext and that he violated what one judge called a ‘‘veritable smorgasbord’’ of federal laws and rules by overriding the advice of career officials who said the citizenship question would cause an undercount of the nation’s population, required each decade by the Constitution.
Noting that Ross had asked the Justice Department to seek the question rather than the other way around, Justice Elena Kagan said that ‘‘it did really seem like the secretary was shopping’’ for help.
‘‘You can’t read this record without sensing that this need is a contrived one,’’ she said.
Ross has maintained that the information is important for several reasons, including enforcement of the Voting Rights Act. He said he carefully considered the advantages and disadvantages of adding the question before making the decision, which Congress expressly empowers him to make.
New York Solicitor General Barbara Underwood, representing the states and local governments who said an undercount would harm them, noted Ross had evidence showing that adding the question ‘‘would not give better citizenship’’ data. Instead, she said, the Census Bureau was taking a risk with a vital function.
‘‘When there is this much uncertainty, then it is arbitrary and capricious to take that kind of risk with the enumeration,’’ she said.
But the conservative justices were skeptical about why they should intervene in an issue Congress seems to have entrusted with the executive branch.
Chief Justice John Roberts noted that historically the census has asked far more than just where people live.
Justice Neil Gorsuch pointed out that the citizenship question was asked on the short form more times than it was not. Justice Brett Kavanaugh said the United Nations advised countries to ask such a question.
The case has generated an outpouring of amicus briefs, filed mostly on the side of the states, cities, counties, and immigrants rights groups challenging the decision.
They say the census has enormous impact. The count determines the size of each state’s congressional delegation. It informs how the electoral districts are drawn for those seats and others, and determines how billions of dollars in federal aid is distributed.
Critics — including experts at the Census Bureau who report to Ross — say adding the question will mean more households containing noncitizens are likely to ignore a request for information. Although the information is confidential, those with ties to undocumented people might not trust the information to the Trump administration, which has taken a hard line on immigration.
Experts calculated that adding the question could mean an undercount of as many as 6.5 million people and cause special harm to urban areas and states with large immigrant populations.