One of the reasons that Kamala Harris and the Democrats lost is that Congressman Jim Clyburn made Joe Biden an honorary Black man. Trump was doing terribly in the primaries before the 2020 election until he came to South Carolina. There Jim Clyburn intervened by endorsing Biden, thereby winning him the Black vote, which won him the primary. From there on, Biden coasted on to victory.

I have no evidence but it seems likely to me that there was some sort of agreement between Biden and Clyburn, that Biden would name a Black person as his vice president, who turned out to be Kamala Harris. While Biden pursued a progressive, Black agenda after election, it backfired against Trump in 2024. Trump waged a campaign that won over many blacks, and thus undermined the emphasis on Black-ness by both Biden and Kamala. The Jim Clyburn endorsement and Kamala Harris' Black-ness did not have the power in 2024 that it had in 2020.