[F.J. Mitchell]

Considering his name, Obama would more likely be a direct descendant of Mohammad, or the reincarnated return of the guy who has been down the well all these years,

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There are various Dunham genealogies on the Internet. One family comes from West Virginia, where Washington had relatives, so it's possible there's a connection.

Considering his name, Obama would more likely be a direct descendant of Mohammad ...

He might not be the only one:

The mathematical study of genealogy indicates that everyone in the world is descended from Nefertiti and Confucius, and everyone of European ancestry is descended from Muhammad and Charlemagne

Source

That may be overstating things, but even the British royal family is said to have had Black (and presumably Muslim or Jewish) ancestors.