It’s tempting to think the House Oversight Committee’s vote this week to hold two Trump cabinet secretaries in contempt is just the latest showdown over documents and “obstruction.” It’s not. This one is all about the Supreme Court.

Oversight Chairman Elijah Cummings would like the public to think this vote was about a refusal by Attorney General William Barr and Commerce Secretary Wilbur Ross to turn over documents related to the administration’s decision to add a citizenship question to the 2020 census. He complained that the administration has “delayed, dissembled” and thwarted committee oversight.

But that’s hard to square. The Justice Department has flooded the committee with information, turning over 17,000 pages of documents, and making officials available for hours of interviews. More telling, the process isn’t over. The department is readying thousands of pages more, and the committee has already scheduled additional interviews. Contempt is usually a way of breaking an impasse; there’s no need for it when an agency is cooperating.

So why the rush? Mr. Cummings’s vote is the left’s latest, desperate effort to get the Supreme Court to stand down from an imminent ruling over that same census question.

Democrats have convinced themselves that if the administration is allowed to include the question, illegal aliens will shy away from the census, resulting in an undercount in urban areas and fewer Democratic House seats. The party is uninterested in the substantive policy reasons for the question. As New York’s Rep. Alexandria Ocasio-Cortez admitted in Wednesday’s hearing: “This determines who has power in the United States of America.”