What would the charge have been? Loitering in DC may have been a misdemeanor, but just coming from a state where some had decided to secede wasn't. There would have had to have been some specific act on Davis's part, so I'm pretty sure he was safe, so far as the law went. He left DC well before he was chosen as POTCSA.
When prosecution for treason was considered after the war, there were all kinds of legal technicalities advanced as reasons not to have a trial. Most of them weren't very convincing. There was no trial because of the political awkwardness. It would have kept the country divided and a jury's verdict couldn't have been reliably predicted.
Until such time as it has, any reference to Lee, Davis, or any other Confederate as "traitors" is merely personal opinion without judicial concurrence. Surely you can understand how some people might find that offensive.
Ditto for Benedict Arnold, I believe. And even Alger Hiss wasn't convicted of treason.
But online, when has something being considered "offensive" put it off-limits?
Last things first. It should not be off-limits. And the person making the charge shouldn't be surprised when he gets pushback.
When prosecution for treason was considered after the war, there were all kinds of legal technicalities advanced as reasons not to have a trial. Most of them weren't very convincing. There was no trial because of the political awkwardness. It would have kept the country divided and a jury's verdict couldn't have been reliably predicted.
What were the technicalities? I'm aware that Chief Justice Salmon Chase warned the administration of the possibility of losing on constitutional grounds, but I'm not convinced that a jury couldn't have been cherry-picked, even in Virginia. Davis was hardly more popular in Virginia than in the North by the end of the war. The administration certainly had no problem getting a Virginia grand jury to indict him in the first place.