This is generally the case, especially in presidential politics. However, the black vote in Democratic primaries is not as monolithic or ideologically fixed as often stereotyped. There is a recent trend of black insurgent candidates doing quite well in or getting their primary base of support from majority-black precincts in downballot races where their primary opposition is a white establishment candidate (Jamaal Bowman, Summer Lee, and Brandon Johnson are a few examples of this phenomenon).
Black voters almost support the black candidate over a white candidate, regardless of ideology. So they supported far-left Brandon Johnson over centrist Paul Vallas and former Republican Eric Adams over establishment progressive Kathryn Garcia.
Yeah, that was what I was trying to get at, sorry. I will also note that many such black candidates have outperformed white insurgent candidates at the national level (for example, while Cori Bush lost the large share of black precincts in St. Louis against Lacy Clay she ran ahead of Bernie Sanders' margins in the 2020 primary in such precincts).
