Very interesting, from a reader:

A couple of thoughts:
The first is, I suppose, of merely a personal interest to me, and that
is that I guess that it’s now absolutely official that if one of your
parents is black and the other is white, you are genetically black, not
white, not both, nor any other more nuanced description. I say that by
way of personal interest (interest, not concern; I really don’t care
what labels people use), since I have two daughters that are pretty much
exactly as “black” as Mr. Obama, their father (me) being a white
American and their mother being a (black) African. I remember that back
in the 70s version of Politically Correct, it was bad to make the “mixed
equals black” assumption, since it was claimed to have derived from the
racist “one drop” rule.
The second is more germane, but links to the first, and that is that
“blackness” is of necessity becoming more an issue of culture than
ancestry, precisely because of the prevalence of people like Barack
Obama and my daughters. For those who wish to preserve some “racial
identity” in the face of the reality of the disappearance of racial
boundaries, the only alternative is a definition of race based on
culture, ideology or behavior (a definition of race based, therefore, on
stereotypes.) Once race is redefined in these terms, “racism” then
automatically also becomes redefined as opposition to a particular
culture, ideology or behavior. But, since “racism” is still seen as an
ultimate evil, it then becomes the ultimate evil to be opposed to
particular ideologies or behaviors (conveniently, those espoused or
practiced by folks of a predominantly left-wing bent.) So, we get the
bizarre situation of a few years ago, when a black friend of mine (or at
least one who was considered black enough in the 1950s to not be allowed
to use a “whites only” waiting room), was accused of being racist
against blacks because he believed that Bill Clinton should be removed
from office (the same Bill Clinton who, by his appearance, would
definitely have been allowed to sit in that waiting room.)
Perhaps this is a strange realization of Dr. King’s dream, people being
judged as “black” based not on the color of their skin, but on the
content of their character (“character” defined as level of adherence to
the objectives of the Congressional Black Caucus, or as level of
personal underachievement, or whatever “acting black” means at a
particular time.)