South Carolina lets anyone 65 or older mail in a ballot for any reason at all. Everyone younger needed an excuse: a disability, a job that keeps you out of the county, a stint in the county jail. On Aug. 18, the Fourth Circuit said that scheme violates the 26th Amendment. Not because mail voting is some newfound constitutional right. Because a state that hands out a voting convenience can’t ration it by birth year.

Most ballot-access litigation turns on the same tired fights over race and residency. This one is different. Grant v. Belangia is a 26th Amendment case, and courts have barely touched that amendment since it lowered the voting age to 18 in 1971. When a unanimous panel actually applies it, conservatives ought to pay attention, even when the immediate winner looks like the other team’s client list.