Calhoun apparently raped his great-grandmother who was one of his slaves.
He did know that before he wrote this NYT article where he reflects on that: https://mobile.nytimes.com/2017/02/10/opinion/get-my-racist-ancestors-name-off-of-yales-campus.html?smid=tw-share&_r=0&referer=https://t.co/SVe0MGAy83