I believe that Frank Marshall Davis wrote about having sex with a 13 year old white girl in his autobiographical sex book, the name of which escapes me. Hmmmm.
Sex Rebel: Black. But we don't know just how "autobiographical" the book was. The porn industry of the day liked to portray its material as really true, but like "Penthouse letters" that wasn't always true. The time line doesn't exactly fit either, since Ann Dunham would have been in Washington state at the time and Barack Obama was born when she was 18.
The funny thing though, is that it was a "fan" who supposedly detected similarities between Sex Rebel by "Bob Greene" and Davis's poetry, so Davis felt compelled to admit his authorship. I don't know if that's true either, but it should give conspiracy theorists hope that they really could uncover the secret author of a book through stylistic similarities.