She identifies as black because most "blacks" are actually mixed with white and / or South Asians if their family comes from the Caribbean. The fact that she is partly South Asian doesn't change the fact that most people perceive her as "black".
So the black self-identification is 100% legitimate.
Of course it is, and it is honestly not even worthy engaging with this point.
But the Trump campaign can't seem to help itself in going all in with this twisted, racist logic, which goes something like the following:
Normal people (straight white men) don’t get to “choose” their “identities,” and everyone has to have one and only one identity. But there are all kinds of cheaters who get to be multiple things when it suits them.
This is unfair to "normal" people (SWM) because the normies don'tget all the special advantages that the Elites have decided to give the people who, instead of being normal, claim to be special, because they’re women, or members of racial/ethnic minority groups, or gay, or trans, etc. etc. etc.
Worse, people like Kamala Harris get to change their identity for social advantage, which normal people can’t do, because they are normal, which she and people like her are not. This is unfair. It's unfair even to the other "identity politics" people because it is cheating even in the unfair to white men system even more.
Back when America was "GREAT", people like her couldn’t get away with this. First, because you just weren't allowed to, and second because no one would want to since if you wanted a really important job you had to be normal.
By being normal we knew you were being picked for merit and not for identity.
Now you have people like her deciding she’s Indian one day and Black the next, like changing outfits, which is another advantage the Elites have given those abnormal people over the normal ones.
Worse, all this changing identities stuff is weird, and not normal, but they are calling the NORMAL people weird, which is also unfair.