Commerce Secretary Wilbur Ross at the White House on June 20. (Mandel Ngan/AFP/Getty Images)

THE TRUMP ADMINISTRATION’S decision to add a question about citizenship to the 2020 Census from the start has looked suspiciously like an underhanded way to depress Democratic representation in Washington. Now a federal judge is saying so, remarking in court this month that there is a strong appearance of “bad faith” and that the Trump administration’s rationale for adding the question appears to be nothing more than pretext.

Eighteen state attorneys general, as well as D.C. and other smaller jurisdictions, are suing to stop the Census Bureau from inquiring about people’s citizenship status, and U.S. District Judge Jesse Furman presides over the case. The suit is young, but Mr. Furman has already said that the challengers made a “strong showing” that the administration’s reasons for adding the question are suspicious. Mr. Furman authorized the challengers to collect records and take depositions.

Mr. Furman pointed to seemingly contradictory statements from Commerce Secretary Wilbur Ross, who oversees the Census Bureau. When he added the citizenship question to the 2020 Census form, he insisted that he did so in response to a Justice Department request for better data on the voting-age population in various parts of the country, which Justice lawyers could use in voting rights cases. Yet in a June memorandum, Mr. Ross stated, “Soon after my appointment as Secretary of Commerce, I began considering various fundamental issues regarding the upcoming 2020 Census, including funding and content,” considerations that would have come before Justice formally weighed in. “Part of these considerations included whether to reinstate a citizenship question, which other senior Administration officials had previously raised.”

It is unclear which “senior Administration officials” pressed to add the question, but former White House political operative and immigration foe Stephen K. Bannon is a likely possibility, given evidence in other court records. Adding yet another reason for skepticism about the administration’s motives, Mr. Furman noted that the Trump Justice Department “has shown little interest in enforcing the Voting Rights Act,” raising questions about why Attorney General Jeff Sessions, a renowned immigration hawk, would be so interested in a major policy change at the Census Bureau.

The real answer is probably that seemingly small changes to the census form can have massive effects on government spending and congressional representation. A lot of federal funding is distributed based on states’ total population. So are congressional seats. Adding a citizenship question on a form sent by an administration explicitly hostile to migrants is highly likely to depress response rates among immigrants, even those who have naturalized. This would make urban centers in blue states look less populous and, therefore, less deserving of money and representation.

Instead of continuing to contest the lawsuit, Mr. Ross should eliminate the new question.