Black voters make up about 20% of all Democratic voters, according to 2016 primary exit polls and 2018 data from the Pew Research Center . Unlike college-educated whites and very liberal Democrats, black voters have consistently been a large portion of the Democratic base. That's partially about how many black voters there are in the electorate, but also about when the states with the highest percentage of black voters in them cast ballots. If they are doing particularly well with black voters, they might be able to count on South Carolina as a backstop. But even if the eventual Democratic nominee doesn't win the black vote, they will still need black voters to vote heavily for them in the general election.

Source: CNN April 05, 2019 09:56 UTC