The Supreme Court’s March 2026 oral arguments in *Watson v. Republican National Committee* provide the primary driver for the 76.5% implied probability that the Court will bar counting mail ballots received after Election Day. During arguments, a majority of justices, including several conservative members, expressed skepticism toward Mississippi’s grace period for ballots postmarked by Election Day but arriving up to five business days later, questioning whether federal statutes setting a uniform Election Day require receipt by that date. The Fifth Circuit had already ruled against such state provisions, and the Court granted certiorari in November 2025. Observers anticipate a decision by late June that could invalidate similar laws in roughly 14 states and D.C. ahead of the 2026 midterms. No final ruling has issued, leaving room for shifts based on the written opinion.