He's done this bit at his rallies for years. I used to watch his rallies frequently to see his new talking points. He would ask the crowd "Do you know what the n word is?" There was a few times when someone in the crowd shouted the actual slur. Then Trump would laugh and say "No. the n word is nuclear." I think he was baiting the crowd intentionally to say the slur.

Here's the nuclear video clip from today.

https://xcancel.com/Acyn/status/1923502695354335542