Democratic Primaries

Just black voters. You don't need the qualifiers. In fact, they make your assertion sound dismissive and misinformed.

Black voters, in general, voted overwhelmingly for Biden.

"moderate white older people"

Same problem. It's not just "moderate white older people". It's college-educated women. It's working-class voters in Michigan and other states. It's surburban Democrats. It's left-leaning independents. It's the majority of pretty much every demographic group outside of young, white men, and even they're not showing up for Sanders in the numbers Sanders asserts.

The dismissiveness shown in your assertions is part of the problem and indicative of why Sanders isn't doing better and why it would be a horrible strategy for November. Write off groups you don't like, you lose.