When Commerce Secretary Wilbur Ross announced that the Trump administration would add a question asking about citizenship to the 2020 census in March, he pointed to a Census Bureau analysis saying there was no empirical evidence that adding the question would cause people not to respond to the survey.

Ross failed to mention, however, that the Census Bureau also offered a clear warning about adding a citizenship question. A January memo from a top bureau official said it would be very costly, harms the quality of the census count, and would use substantially less accurate citizenship status data than are available from administrative sources. The memo said adding the citizenship question would cost at least $27.5 million.

The memo, written by John Abowd, the Census Bureaus associate director for research and methodology and its chief scientist, was disclosed in a Friday filing among more than 1,000 pages of documents as part of a lawsuit challenging the addition of the question. The documents provide new details about the decision to add a citizenship question and raise significant concerns about the justification for the change.

Ross instructed the Census Bureau both to add a citizenship question and to use data from other federal agencies to supplement what the census collected. But a separate Abowd memo points out that the Census Bureau was making data analysis more complicated by adding the citizenship question, rather than just using the existing agency data.

Abowd noted that, regardless of whether the 2020 census asks about citizenship or not, it will have to impute citizenship status for those who dont respond. Census officials expect some degree of error in making this guess, but when making these kinds of predictions, statisticians usually expect the error to be randomly distributed. Adding the citizenship question, Abowd said, makes it more difficult to make those predictions because the error rates are higher among noncitizens, who are more likely to not respond or answer incorrectly.

The memo is significant because one claim raised in several of the lawsuits is that the decision to add the question violates federal law because it is arbitrary and capricious and abuses the departments decision-making authority.

Ross and the White House have justified the decision by claiming the Department of Justice needs better citizenship data to enforce the Voting Rights Act. Former top Justice Department officials question whether thats true , saying the department has long had the data it needs to adequately enforce the law. The Voting Rights Act was passed in 1965, but the decennial census has not asked about citizenship since 1950.

Ross defended the decision in a statement.

The administrative record shows that the Department of Commerce took a deep dive into the surrounding legal, policy, and program considerations prior to reinstating the citizenship question on the decennial census, as the question had been included for decades prior to 2010, he said. The United Nations recommends that all countries collect citizenship data. In fact, included in the production is a 2014 letter from the Obama Administrations Department of Justice noting that citizenship data is needed for the DOJs Civil Division cases.

The Justice Department made the request to the Commerce Department for the citizenship question in a Dec. 12, 2017, letter. But the newly disclosed documents also show that Ross discussed adding the question months earlier, in July, with Kansas Secretary of State Kris Kobach. Kobach, a Republican who ran Trumps now-dismantled voter fraud commission, has championed one of the most restrictive voting laws in the country and is known as a staunch conservative on immigration issues.

Kobach emailed Ross in July 2017 to follow up on an earlier conversation the two men had about adding the citizenship question. Kobach wrote in a follow-up email to a top Ross aide that he and Ross had previously spoken at the direction of Steve Bannon , who was then serving as a top aide to President Donald Trump .

This lack of information impairs the federal governments ability to do a number of things accurately. It also leads to the problem that aliens who do not actually reside in the United States are still counted for congressional apportionment purposes, Kobach wrote to Ross, referring to the fact that the decennial census does not currently collect citizenship data. Kobach later followed up with Wendy Teramoto, Ross chief of staff, and appeared to have spoken with Ross on the phone again.

The correspondence between Ross and Kobach is likely to add fuel to claims by critics who say the decision to add the citizenship question has nothing to do with the Voting Rights Act. Instead, they say, it is an effort to reduce census participation by immigrants, who might be fearful of giving the Trump administration any data on their immigration status. An inaccurate count would have severe consequences in states with large immigrant populations because census data are used to calculate electoral districts and allocate hundreds of billions of dollars in federal funds.

Kobachs email to Ross also highlights a conservative push to change the way electoral districts are drawn. Currently, districts are based on the total population in them, but officials like Kobach and Rep. Steve King (R-Iowa) have insisted that they should be based only on the citizen population. Alabama is suing the bureau not to count unauthorized immigrants as part of the data used to determine how many members of Congress each state gets. But the 14th Amendment says that congressional representation shall be based on the respective numbers of the states counting the whole number of persons in each state. The language of the amendment makes no distinction between citizen and non-citizen.

These documents make clear what we already knew career staff at the Census Bureau warned the political leadership at the Commerce Department that the inclusion of a citizenship question would depress census response rates, increase costs, and diminish the quality of census data, Vanita Gupta, president and CEO of The Leadership Conference on Civil and Human Rights, said in a statement. Its also clear that the citizenship question was added to advance the agenda of operatives like Steve Bannon and Kris Kobach. The Secretarys decision memo was simply a smokescreen to justify a politically motivated change to the census. The conference has lobbied hard against adding the citizenship question.

A Department of Commerce spokesperson denied that Kobach had swayed the decision on the citizenship question.

The Kobach email is one out of over 500 pages of stakeholder records produced in the administrative record. The notion that Secretary Ross decided to reinstate the citizenship question in response to a single email is clearly disproved by the robust administrative record, the spokesman said.

CORRECTION: A previous version of this article inaccurately transcribed comments in a Census Bureau memo referring to administrative data. The quote referred to accurate citizenship data.