Many people believe that determining who is 'black' is rather easy, a task simplified by the administration of the one-drop rule. Under the one-drop rule, any discernible African ancestry stamps a person as 'black.'
The idea of the mulatto has been a gathering point for a wide variety of racial prejudices, fears, myths, and speculations.
So long as procreation stems from parents of the same race, appearance and lineage are typically congruent. Interracial unions give rise to added complexity. Interracial amalgamation will produce some individuals whose features diverge from those commonly ascribed to the races of their ancestors.
I think that many black people thought this would be a wonderful and extraordinary thing, for a black family to occupy the White House. Not only black people; a lot of white people thought that, too, but particularly black people.