Barack Obama is not half black. If elected, he would be the first Arab-American President, not the first black President. Barack Obama is 50% Caucasian from his mother's side and 43.75% Arabic and 6.25% African Negro from his father's side. While Barack Obama's father was from Kenya, his father's family was mainly Arabs.. Barack Obama's father was only 12.5% African Negro and 87.5% Arab (his father's birth certificate even states he's Arab, not African Negro).
Barack Obama Sr. was born in Kenya.
He was descended from the Luo tribe that inhabited Kenya and Tanzania.
He was as much an atheist as he was an Islamist.
To call the man a Muslim is to call Ray Franz one of Jehovah's Witnesses.
As for what percentage of him was Arab, perhaps some photos would be helpful...