Race more important to black voters

So says Juan Williams:

In a Wall Street Journal poll last month, 8% of white voters said outright that race is the most important factor when it comes to looking at these two candidates -- a three percentage point increase since Mr. Obama claimed the Democratic nomination. . . . Race is even more important to black voters: 20% say it is the top factor influencing their view of the candidates. . . . All this contributes to the idea that the presidential contest will boil down to black guy versus white guy.

Maybe David Gergen can explain this.