Wilbur Ross, U.S. commerce secretary, at March 14 House Oversight Committee hearing in Washington, D.C., on allegations by committee Democrats that Ross has given misleading testimony on multiple occasions to Congress about the citizenship question to the 2020 Census. (Andrew Harrer/Bloomberg)

A SECOND federal judge ruled on March 6 that the most consequential decision Commerce Secretary Wilbur Ross has made drips with bad faith. The conclusion was forceful and persuasive. The Supreme Court now should stop Mr. Ross from abusing his powers.

U.S. District Judge Richard Seeborg found that Mr. Ross committed “the definition of an arbitrary and capricious governmental act” when he ordered that 2020 Census forms include a question on respondents’ citizenship status. Even small-seeming shifts in census response rates can have major effects on how much federal money states and cities receive, and on how many congressional representatives and electoral votes states get. The process must be guided by experts and based on methods insulated from political considerations.

Mr. Ross tried to force the opposite. Mr. Seeborg concluded that “despite unrefuted evidence produced by the professional staff of the Census Bureau that inclusion of a citizenship question would likely result in a significant differential decline in self-response rates within noncitizen and Latino communities and that the requested data could be obtained by other means, Secretary Ross insisted upon adding the citizenship question to the census.”

In order to do so, he engaged in “a cynical search to find some reason, any reason, or an agency request to justify that preordained result.” He turned to the Justice Department, persuading the agency to request that the decennial census collect citizenship data, in “an effort to concoct a rationale bearing no plausible relation to the real reason, whatever that may be, underlying the decision.” It is not difficult to discern the most likely reason. Mr. Ross — or his co-conspirators in the Justice Department and the White House — sought to sabotage the census count, discouraging responses from immigrants. Lower immigrant response rates would lead to less federal money and political representation for areas that lean Democratic.

In fact, because Mr. Ross’s move “affirmatively interferes with the actual enumeration and fulfills no reasonable governmental purpose,” Mr. Seeborg found, it violates the Constitution’s enumeration clause, which mandates a national census every 10 years. This goes even further than U.S. District Judge Jesse M. Furman’s strongly worded ruling against Mr. Ross in January.

The Supreme Court announced last month that it would consider the census question this term, which means it will render a decision by the end of June. As Mr. Seeborg and Mr. Furman argued, the record of Mr. Ross’s misuse of authority is clear. The justices have their pick of reasons to forbid the Commerce Department from sabotaging the census.