The NYT:
When a handful of liberal advocacy organizations convened a series of focus groups with young black voters last month, the assessments of Donald J. Trump were predictably unsparing.
But when the participants were asked about Hillary Clinton, their appraisals were just as blunt and nearly as biting.
“What am I supposed to do if I don’t like him and I don’t trust her?” a millennial black woman in Ohio asked. “Choose between being stabbed and being shot? No way!”
This type of story used to be the mainstay of political reporting. Anecdotal, based on interviews that may or may not be representative.
Certainly it is true that Sanders broke even with African Americans under 30. Beyond that it is hard to know how true it is. The cross-tabs in polling are very small. Moreover polling has tended to understand Democratic Performance among African Americans. It is clear that in some types of polling (Robo-pollsters) people lie about their race.
The article suggests, and I think this is right, that it isn’t an issue of percentage but margin, which in turn is dependent.
But without real data this is all guesswork.