This is how voter intimidation worked in 1966: White teenagers in Americus, Ga., harassed black citizens in line to vote, and the police refused to intervene. Black plantation workers in Mississippi had to vote in plantation stores, overseen by their bosses. Black voters in Choctaw County, Ala., had to hand their ballots directly to white election officials for inspection.

This is how it works today: In an ostensible hunt for voter fraud, a Tea Party group, “True the Vote,” descends on a largely minority precinct and combs the registration records for the slightest misspelling or address error. It uses this information to challenge voters at the polls, and though almost every challenge is baseless, the arguments and delays frustrate those in line and reduce turnout.