I thought I answered it by stating that Lee was covered by his parole agreement.
Davis was not covered by a parole agreement as far as I know, until he accepted parole after he was released, and accordingly before that could have been legally tried and hung. Prosecutor’s discretion was applied, recognizing that when two officials committed similar acts, their treatment should be similar. I look on that as an act of mercy by the victorious federal government.
Davis’ justifications of pretended unilateral secession at pleasure fail. The entire federal constitution, to include the amendment process, and the requirement to resolve disputes using the supreme court, was a limitation on state sovereignty agreed to by the states when they accepted the Constitution. To pretend that later a state could overturn their sovereign agreement to those limitations would be a ex post facto limit on the sovereignty of the states which agreed to the Constitution.