By challenging Obama for the black vote - by promising to go door to door in South Carolina in minority neighborhoods, for example - Bill is highlighting the question: Will Obama carry the bla ck vote? Of course, he will. He leads, 4 to 1, among African-Americans now.
But by making that the central question, Obama's South Carolina victory will be hailed as proof that he won the African-American vote. Such block voting will trigger the white backlash Sen. Clinton needs to win.
Once whites see blacks voting en masse for a black man, they will figure that it is a racial game and line up for Hillary. Already, she carries white voters by 2 to 1.
The Clintons can well afford to lose South Carolina as long as the election is not seen as a bellwether of how the South will vote but as an indication of how African-Americans will go. It's a small price to pay for the racial polarization they need to win.
So to seize the limelight, take Hillary out of the line of fire, and to call attention to his head-to-head battle with Obama for the loyalty of America's blacks, Bill Clinton is seeking all the coverage he can get, positive, negative o r neutral.