I would tell that to Lee.
As I remember it they were political rivals.
Also John Adams said much of the same thing when he was feeling ignored and not getting the proper credit for his role.
Again politics not academics!
So? Technically, many of the fictional works are plagiarism as well even if they intended it to be repeated. When it’s outright copied, it’s plagiarism. I would say it if someone, say, copied plotlines to my stories, even if I actually approved of them and given the go-ahead to do so. Heck, George Lucas plagiarized Buck Rogers, and I’m pretty sure they gave the go-ahead.
Either way, it still doesn’t change that Thomas Jefferson did indeed plagiarize, not just repeated some themes, but outright lifted word for word some stuff. And quite frankly, I’d consider Thomas Jefferson cheerleading the Jacobins and eviscerating William Short, a guy he considered his own son, to be far more damning that MLK being duped by Communists.