A trove of documents brought to the attention of the Supreme Court on Thursday makes it hard to see the Trump administration’s efforts to include a citizenship question on the 2020 census as anything but a partisan power grab.

The court will decide before the end of June whether Wilbur Ross, the commerce secretary, was justified under federal law in adding the citizenship question — a move that would nearly certainly lead to a serious undercount of Hispanics in immigrant-rich communities . During a hearing on the case in April, it appeared that a majority of the justices was prepared to allow the administration to include the question.

But the explosive new evidence disclosed by the plaintiff s in the case ought to give the justices pause about the ruling they’re about to issue. This is one of the most consequential cases before the court this term. The decision on it will have far-reaching effects on the distribution of political power and federal funding across the country for the next decade and beyond.

According to the plaintiffs who brought the New York challenge to the citizenship question, Mark Neuman, a key adviser to Mr. Ross on census issues, and John Gore, a Justice Department official who oversees voting rights enforcement, gave false or misleading testimony during the course of the litigation about why the Trump administration was so intent on including a citizenship query in the decennial count.