Barack Obama Sr. (the Senator's father) was a Kenyan born in 1936, when Kenya was still a British colony.
When was the last time the United States had a President who was that close to the British colonial experience? That is, when was the last time a President was only one generation removed from direct British rule?
Some quick Wikipedia-ing suggest Lincoln or Andrew Johnson.
Also, kind of an inside joke among my friends: Obama Sr. was a political opponent of Jomo Kenyatta. A clash with African strongmen is not generally a career-enhancing move, nor was it for Obama Sr.