Is claiming someone has committed a crime (one that's on the books and has a clear legal definition) not a crime in itself in the USA?

It's one thing to state:

"In my opinion, what NN has done amounts to treason against XX"

and another to say:

"NN has committed treason".

I'm not a lawyer or a legal scholar or anything like that, but I do know definitions of words matter a lot, and in a legal context even more so. I do know that here, claiming that someone is guilty of a crime when there's no conviction, can be a criminal act.