Two things:
1) You might not be able to comprehend it, because you dropped the word "white" from your sentence. Put it back in, and it becomes easier to comprehend.
"What I cannot comprehend is why a large number of *white* women would vote for somebody that is obviously against women's rights in general, but for white nationalist policies."
A large number of Black women *do not* vote for somebody that is obviously against women's rights in general, but for white nationalism.
1/N