Logically it still made sense, IMO. If he's half black and half white, while all previous presidents were only white, then the black part is the discriminating factor one could highlight as a success to deviate from the previous norm.

If you wanted to highlight this deviation without leaning in on the black part, you would have had to use something like “not fully white”, which would have been explicitly subtractive and therefore much worse.

Of course one could simply ignore the skin color completely, but I also see empowering in highlighting this shift of breaking an otherwise strict all white run.

This is because the American slave owners wanted to be able to sell their own children.

After raping a slave, if she got pregnant they could free their child or keep them as a slave.

Thomas Jefferson's concubine, Sally Hemmings, was probably 3/4 white, and at least 1/2 white. Her granddaughter created a scandal when she 'passed' for white.

If an american tries to call themselves Native because they are 1/32 Native, people laugh at them. But up until a few years ago, being 1/64 Black made you Black.