One of the rather thin arguments against calling Robert E. Lee a traitor is that to be a traitor, you must first be a citizen. In 1860 there was no legal definition of citizenship in the United States. It's hard to prove that Bobby Lee was an American citizen, so how can we prove that he was a traitor?
Of course, Lee had served in the American army, and he had sworn the usual oath of allegiance to the United States many times to guarantee his loyalty. In return he had gotten a free college education, a job, etc.
Citizenship was finally defined in 1868, after the Civil War, in the fourteen amendment. "All persons born or naturalized in the United States . . . are citizens of the United States and of the State wherein they reside." So I did not become a citizen until I was born in Compton, California. Here is something for originalist Republicans to work on. Why hasn't citizenship been conferred on fetuses?