I think he knows. It explains much of his behavior regarding his Half Brother living in a shack in Kenya (Hey Bro! Spread some wealth around why doncha?) and his impoverished Aunt living in Boston.
He doesn't care because he knows they aren't blood.
I give up who is Obama’s father?
I give up who is Obama’s father?
I give up who is Obama’s father?
Do you think Toot told him? And when?
See, I’m not even sure SAD knew who the father was.