Louisiana added a grandfather clause to its constitution in 1898, and other Southern states followed. The date mattered. Before the Reconstruction Acts of 1867 and the 15th Amendment in 1870, almost no Black men in the South could vote. Tying the exemption to that date let states keep literacy tests and property rules on the books while sparing white men who could not meet them.
In Guinn v. United States (1915), the Supreme Court ruled that Oklahoma's grandfather clause violated the 15th Amendment. It was one of the NAACP's first legal victories. But states kept other tools, including poll taxes, white primaries and discretionary literacy tests, so Black disenfranchisement continued for another 50 years.
The phrase lives on in everyday speech. Being "grandfathered in" now means an older arrangement is exempt from a new rule. Few people who use it know the term began as a device to keep Black men from voting.