Early in the campaign, in 2007 in fact, Rush Limbaugh (no referring-link love here) tried to claim the phrase “Magic Negro” and attach it to our now soon-to-be President. He pulled it from an LA Times editorial, which I understood to be about public perception and expectations of Barack Obama.
The Magic (or Magical or Mystical) Negro, a stock character of film and literature always subservient to the needs, goals, and personal growth of the white (usually male) protagonist, is a racially-infused construction of the older mythic tradition of the Companion.
As the Hero sets out on his (or her) journey, he often acquires up to three companions, frequently possessing magical powers, who assist him on his quest. The Companion may be a dangerous wild man or talking animal, or even a wise though non-magical servant.
Barack Obama does not fit the construct of a Magic Negro. He is not a companion to a protagonist, he is the protagonist. It is as the Hero that he carries the hopes and expectations of the nation. His quest is to lead the nation.