First off, the word was offensive and known to be offensive 50 years ago, 100 years ago, and 150 years ago. I can find you books from 1860 that say, “Hey, thats offensive to blacks”.
It’s not like people who used it in 1960 didn’t know it was offense to blacks. They just didn’t care. People who use it now still don’t care.
Second, how is there any doubt that Trump is a bigot?