The Supreme Court ruled 5-4 Monday that states can count mail-in ballots that arrive after Election Day as long as they were postmarked by Election Day, rejecting a Republican National Committee challenge to Mississippi's law. This decision protects vote-by-mail systems in more than half the states and preserves a crucial accommodation for ballots delayed in transit. The ruling is a significant setback for GOP efforts to tighten election administration in ways that would disenfranchise voters whose mail arrives late through no fault of their own.