To my understanding, it's a play on words, and it's the word race that's in focus. The word race has two meanings: i. a competition, and ii. any people united by common history, language, cultural traits; moreover, closing [the] divide is an idiom meaning to converge; i.e., bring together, opposite of diverge, separate:
“Poll Finds Obama Isn't Closing Divide on Race."
(a) The voters remain divided (Obama isn't closing the divide on the race (sense i.)
(b) The division is based in race (sense ii.)