All networks and the AP called it the second the polls closed. Exit polls show Hillary winning 84% of the African American voters, which makes up 67% of the primary vote in South Carolina. Hillary won across all age groups, young and old, though young voters (i.e voters under 30) made up only 13% of the vote in South Carolina, which is the lowest of all contests so far.
Update: Wow. Updated exit poll has Clinton up 87-13 among black voters, up 53-47 among white voters. Implies a 75-25 victory for Clinton.