I don't know. Trump has never been one to back down from a challenge, and to change now would just be phony, and he's got a plate full of phoniness to deal with already.
Donald.....STFU about everyone else and just go after Hitlery!!
Maybe back it down to the level of, "I was attacked (or "challenged"), I responded, let's leave it alone."
As for the Khan thing, he could/ought say something like, "He attacked and smeared me unprovoked, I responded much more gently than I usually do out of respect for Capt. Khan, I'm going to let it go. He's a grieving father, he can say whatever he wants about me and I'll leave it alone, to a point. If it gets ridiculous, I have a right to defend myself, and I will."
Donald.....STFU about everyone else and just go after Hitlery!!