Continuation of a 400 year old tradition of Virginian Elites. When sons of plantation owners reached the age of 16, they got a horse, a man servant who took care of the horse and served as a valet, and a young female slave who was intended for sexual romps.
Virginian Democrats are quite the traditionalists.
Truth be told, there was a lot of competition for the position of designated sexual romper or, as it was called back in the day, bed wench.
It got one out of field work and into light housework plus a few bed wench type activities. Many of the older ladies would coach the young teenage girls on how to angle for such a position.
Almost every descendant of African American slaves will find trace elements of white DNA in theirs. The few exceptions are those who either:
The ultimate goal was to do what Solly Hemmings did, dilute the bloodline to the extend you could get emancipated and pass yourself off as white. Of course, that is no longer an advantage today and it, thus, why half-breeds like Colin Kapernick, Barack Obama and Ben Jealous instead pass themselves off as Black.