Even today, the percentage of registered and actual voters who are black in Georgia and North Carolina — and most likely throughout the South — trails the percentage share of the adult population who are black among those old enough to have been disenfranchised for one election or more. The gap closes among voters who reached voting age soon after the voting rights law was enacted; younger black voters have higher rates of participation in the electoral process than nonblack voters, perhaps because of Mr. Obama’s candidacy and presidency.

Jim Crow is a chapter in a history book for younger people, and probably a distant memory for those old enough to have lived through part of it. But the voter registration data is evidence that the effect of Jim Crow remains for black Americans who grew up in the segregated South. They were denied access to the opportunities afforded their white counterparts, and although the end of de jure segregation restored those opportunities, it did not provide them retroactively. The direct effects of Jim Crow may endure as long as the generation that grew up under its influence remains.