The Supreme Court ruled on Friday that the Trump administration can deploy an expansive online system that combines citizenship information, Social Security numbers and other sensitive data about millions of Americans, including to allow states to use it to hunt for ineligible voters. Critics fear that using the system could result in the purging of large numbers of valid voters from state rolls, if states choose to use it ahead of the midterm elections. The majority concluded that a lower-court ruling that had blocked the Trump administration from rolling out the system was improper because it inhibited “the federal government’s efforts to assist state and local agencies in the proper administration of the midterm elections.”

The emergency ruling was unsigned and gave no vote count, but the court’s three liberal justices joined in dissent. Justice Ketanji Brown Jackson emphasized that the majority’s decision created the conditions for some states to cancel the voter registrations of at least some recently naturalized citizens or to force them to provide proof of citizenship before voting. The decision came after the justices had dealt the administration a major setback this month, when the court’s majority blocked the government’s plan to require the Postal Service to screen mail-in ballots.

In March 2025, Mr. Trump signed an executive order directing several federal agencies, including the Department of Homeland Security and the Social Security Administration, to pool their records into an online tool that state and local officials could use to verify the citizenship and immigration status of registered voters. Several legal challenges followed, including a lawsuit by voting rights groups. In June, a federal judge in Washington blocked the Trump administration from allowing states to use the online system to screen their voter rolls.