Which goes more towards pointing out Davis's abysmal understanding of the law and the Constitution tahn anything else. The Constitution defines treason. What exactly had Davis done that qualified? Resigning from the Senate isn't treason. Advocating secession isn't treason. The South hadn't started the war yet. What treasonous act had been committed?
Now assuming for the sake of arguement that Davis had committed treason. He would have been arrested, tried in federal court, convicted, appealed, conviction upheld, and appealed again before it would have gotten to the Supreme Court. The rebellion short-circuited that path just a little bit.
No, but many of Jefferson Davis's contemporaries claimed that actual secession was treason...and that's exactly what Davis said he was joining. Mississippi had already seceded.