Whence Obama's Accent?

Listen carefully to Barack Obama, and what you'll hear is a faint southern (whitish) accent, located roughly midway between a northern white (non)accent and a black accent. It's not quite black enough to scare the white electorate, though it does have a tendency to turn several shades darker when he's speaking to an all black audience. But it's not white enough to make him sound like a Tom or an effete Ivy leaguer.

So the question becomes, just where did he acquire this quasi-Southern accent? Did he get it from his Kenyan father, who disappeared from his life when he was two? From his Kansan mother? From his Kansan grandparents, who raised him while his mother went gallivanting around the world? From his schoolchums in Indonesia? Or is that the way they speak at Punahou, the exclusive Hawaiian prep school he attended?

One can't help but suspect that his accent, like everything else about him, was carefully constructed for maximal electoral value.