As I noted in March, the Trump Administration’s decision to add a citizenship question to the 2020 census will likely make the count less accurate and costlier. A newly released internal memo shows that the Census Bureau’s chief scientist told Administration officials the same thing — and also told them that the question was unnecessary to meet the Administration’s stated goals.

We’ve explained that such a question could have a chilling effect on responses by immigrants and others, especially in the current political environment, due to fears of how the government would use the information.

In the memo, dated January 19, 2018, Chief Scientist John Abowd warned that adding a citizenship question “harms the quality of the census count.” “Three distinct analyses support the conclusion of an adverse impact on self-response and, as a result, on the accuracy and quality of the 2020 Census,” the memo adds. The question would also likely drive up follow-up costs by at least $27.5 million as the Bureau tried to make up for a falling response rate.

The Administration says it’s adding the question to generate local counts of citizens, which it claims it needs to enforce voting rights laws. But, Abowd explains, officials could obtain this information from existing Social Security Administration data and other government records — an alternative that would be more accurate, less costly to taxpayers, and less burdensome for the public than filling out another census question.