Folks, the margins of error in individual state & national primary polls on support among black voters, or Hispanics, are often very high (e.g. around +/- 10%). That why a candidate can be at 19% in one poll and 5% in another or whatever. People can make too much of these swings.
And that's assuming that small sample sizes are the only problem with estimating support among black or Hispanic Democrats, which they aren't. Getting truly representative samples of black or Hispanic voters can be a challenging problem.
If you aggregate across a range of polls, then so far, no candidate apart from Biden *really* seems to have made a lot of headway among African-Americans. And that's reflected in his fairly clear and consistent lead in SC, where sample sizes among black voters are a lot larger.
