The second trend is that Cuomo's lead is indicative of is the continually poor showing by progressive insurgents among black voters.

Cuomo is leading across pretty much all demographic groups, but he's particularly strong among African-Americans. Although no crosstab of black voters was available in the Quinnipiac poll, an earlier Siena College poll put Cuomo's margin over Nixon among black voters at 74% to 17%.

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Why are progressive insurgents struggling with black voters? Black Democrats are more likely to consider themselves moderate or conservative than other Democrats. They also are more likely to identify as Democrats instead of independents who lean Democratic.

That is, they are far more comfortable with the more moderate Democratic establishment than other Democrats are, especially whites.

Now obviously it's possible for progressive challengers to win a primary even with this difficulty (see Ocasio-Cortez). But until candidates like Nixon and Sanders solve their black voter problem, they're going to be limited in their electoral victories.