WASHINGTON The Supreme Court appeared willing to allow the Trump administration to add a question asking every American household to identify citizens and noncitizens on the 2020 census .

The court appeared split along ideological lines during oral arguments Tuesday. The courts more conservative justices, including Chief Justice John Roberts, noted that the census asks many questions beyond simply counting people and that it didnt appear unreasonable to add a citizenship question. The courts more liberal justices noted that Commerce Secretary Wilbur Ross had failed to ever articulate a rationale for why adding the citizenship question was the best way to go about getting the data the Trump administration wanted.

The Census Bureaus own experts estimate that an additional 5.8% of households with a noncitizen are unlikely to respond on their own to the census, which goes out to every American household just once each decade. That translates to approximately 6.5 million people.

There are always going to be trade-offs between adding a question and gathering data, U.S. Solicitor General Noel Francisco argued. But in this case, Ross had made the calculation that the benefits of asking the citizenship question specifically outweighed the cost of a declining response rate.

The Trump administrations official rationale for adding the question was that it needed better data to enforce the 1965 Voting Rights Act. Although the Justice Department has failed to clearly explain how the existing quality of data would hurt its voting rights enforcement efforts, Roberts noted that the census has long asked demographic questions unrelated to counting the actual population and wondered whether it would hurt the departments efforts to have such data. He asked New York Solicitor General Barbara Underwood, who was representing the plaintiffs in the case, whether having the data wouldnt support enforcing the landmark civil rights law.

Do you think it wouldnt help voting rights enforcement? The CVAP, Citizen Voting Age Population, is the critical element in voting rights enforcement, and this is getting citizen information, he said. Underwood said there was no evidence that Ross specifically needed to add the citizenship question to get the data he needed.