The Supreme Court’s March 2026 oral arguments in *Watson v. Republican National Committee* showed a clear majority of justices skeptical of state laws permitting mail ballots postmarked by Election Day to be counted if received days later. Challengers, including the RNC, contend that the 1845 federal statute setting a uniform Election Day requires ballots to be received—not merely cast—by that date, preempting grace periods in roughly 15 states and D.C. Lower-court precedent and questions from conservative justices during argument reinforced expectations of a ruling striking down Mississippi’s five-day receipt window, with a decision anticipated by late June. Traders have priced this procedural and jurisprudential trajectory into the 73.5% implied probability for a bar on post-Election Day counting.