General Discussion

Different heritages and different preferences in word usage. I am more familiar with Native American word preferences than with word preferences among Black Americans. For example, it is not necessarily offensive to use the plural Native Americans, depending on context. If used to lump them all as one culture/religion/customs, it is offensive because there are many different Native cultures. But, again, context matters. And people are individuals, so not all Native Americans feel the same about word usage. But "Red" or "Red Indians" can be offensive in ways that Black or White are not.

Since the Seneca Nation of my heritage is matrilineal, and it comes from my father, I am identified as White, with my White European-American mother. Personally, I have never found the plural, Whites, offensive. But I can't speak for all White people. Or for all Seneca or all Native American people.

I can easily see Trump's use of "THE Blacks" as offensive, using the article in front of the word "Blacks" as he usually does, but did not recognize the word "Blacks" by itself as offensive until you mentioned it.