WASHINGTON, Aug. 25 -- Three months before Americans vote in November's midterm elections, the Supreme Court handed President Donald Trump a preliminary victory on Monday, clearing the path for his executive order limiting mail-in ballots to proceed in states where it had been blocked. The 6-3 ruling, split along conservative-liberal lines, lifted a nationwide injunction and sent the legal battle back to the lower courts without addressing the constitutional question at its center.

The executive order, signed in March, directs the Department of Homeland Security to build a federal voter eligibility list and instructs the U.S. Postal Service to deliver mail ballots only to people on that list. The effect, if fully implemented, would shift...