I'll have to look for a decent on-line source, but ...
Obama isn't much African-American. He's 1/8th or at most 1/4 African. Obviously 1/2 Caucasian. Then 1/4 or 3/8ths Arab.
Abraham Lincoln apparently had more African blood than Obama.
Then I think, but I'd have to find the cite again, that Andrew Jackson had a lot of African blood, to point that his brother was sold into slavery.
The suggestion is that his father was not the man reported to be his father, because his 'father' died a year before he was born. According to the Hermitage and its geneology, his father died 15 days before he was born. (MArch first 1767 vs March 15 1767). If his older brother Hugh was sold into slavery, he was released at some point before the revolutionary war so he could die at the battle of Stono Ferry. Andrew Jackson may not have had a great childhood, but he certainly wasn't raised as black. Just like all the others mentioned, none were raised as black. But apparently the evidence on Jackson is quite iffy, if not downright non existent.
Jefferson is more likely the white father of illegitimate black children. He destroyed his mother's stuff, not his dad's and his dad was the one that would need to be hidden, since he was the one that was supposedly a 'mulatto'.
Barack Obama's father is quite dark, he pretty much looks like a very dark black african. All the names on the genoelogy I found (most of them were from his mother's family, were all very african vs arab. Besides, there are alot of black african muslims. That's part of what is happening in Dafur. Being Muslim doesn't make one arab.)