 His maternal grandfather was the Presbyterian preacher Robert Jefferson Breckinridge (1800–1871), the son of John Breckinridge, a former United States Senator and Attorney General.Warfield's uncle was John C. Breckinridge, the fourteenth Vice President of the United States, and a Confederate general in the American Civil War.A fourth cousin twice removed of his was Wallis Warfield Simpson, for whom Great Britain's King Edward VIII abdicated his throne in order to marry.