President Trump has been trying to restrict mail voting. The Supreme Court has now weighed in for the first time on an executive order on mail-in voting Mr. Trump issued in March. But the ruling — and the slew of challenges to Mr. Trump’s order — are confusing. No one is sure exactly what happens from here, or how it may affect the midterms.

The executive order directs the U.S. Postal Service to restrict mail-in ballots. It also authorizes the Department of Homeland Security to create state-by-state citizen lists to help determine voter eligibility. For now, it appears the Department of Homeland Security can proceed with compiling lists. But another court order blocks the Postal Service from moving ahead with plans to restrict who can receive a ballot by mail.

Trump is trying to leverage the federal government to control mail voting. Mr. Trump has long falsely claimed that mail-in balloting leads to fraud, and he blames a pandemic-era increase in the practice in 2020 for his loss in that year’s presidential election. The president signed an executive order on March 31 directing the Postal Service to deliver ballots only in states that hand over voter data to the federal government.

The Supreme Court acted on Monday — but only preliminarily. Dividing along ideological lines, the justices found that a legal challenge by Democratic state attorneys general was premature, because the government had not yet finalized its plans. The court did not weigh in on the legal merits of the executive order. The justices cautioned that they had not determined whether the president’s directive would “necessarily be lawful” once those plans were complete. The legal fight remains fluid, with multiple lawsuits pending.