“My children deserve the right to know from whom, where and what they have come,” Ms. Washington-Williams said. “I am committed in teaching them and helping them to learn about their past. It is their right to know and understand the rich history of their ancestry, black and white.”

Measuring her emotions, Ms. Washington-Williams explained that her mother was Carrie Butler, a teenage maid in the Thurmond household in Aiken, S.C., in the 1920s, when Mr. Thurmond, the son of a wealthy lawyer, was in his early 20s. She would go on to say in interviews that not until she was 13 and being raised by an aunt did she learn that Ms. Butler was her mother. Several years later, after her mother took her to meet him for the first time, she learned that her father was white.

“You,” he said to Ms. Butler, “have a lovely young daughter.”

After that meeting, Mr. Thurmond, who did not yet hold elected office, delivered $200 to his daughter, using go-betweens.

In 1948, the year Ms. Butler died at age 38, Mr. Thurmond, then the governor of South Carolina, ran for president on a segregationist platform.