“The electorate’s choice is made when voting is complete, not when ballots are received,” Justice Amy Coney Barrett wrote in the majority opinion.
In Watson v. RNC the Supreme Court upheld Mississippi’s grace period for ballots postmarked by Election Day, 5-4, with Barrett writing for the majority. The practical win is real. Grace-period laws in 14 states plus D.C. survive, so a ballot mailed on time still counts even when the postal service runs slow. The challenge was an attempt to throw out on-time votes over a delivery date the voter does not control. It failed, and that protects the people most likely to be hit by a late delivery.