The Supreme Court is hearing a major elections dispute, Watson v. RNC, regarding whether federal law prevents states from counting mail ballots that are postmarked by Election Day but received by election officials later. The case involves Mississippi's deadline for late-arriving mail ballots and whether its law, along with similar measures from 13 other states, conflicts with federal statutes that set Election Day as the day the ballot box closes. The Republican National Committee is challenging these grace periods, arguing that they are an exercise of states' authority to set rules for federal elections. The Supreme Court's decision on the case is expected before the November midterm elections.