“Under our constitutional structure of separated powers, the nature of presidential power entitles a former president to 1) absolute immunity from criminal prosecution for actions within his conclusive and preclusive constitutional authority,” Chief Justice John Roberts wrote for the court. “And he is entitled to 2) at least presumptive immunity from prosecution for all his official acts. There is 3) no immunity for unofficial acts”, and “not everything the President does is official." (AP)

So they establish a three-part test. Trump was still in office as the defeated, illegitimate president from Nov. 3, 2020 -Jan. 20, 2021. Which of his subject actions during that interregnum were “within his conclusive and preclusive constitutional authority”, i.e. where there is no doubt of his, and his alone (“preclusive”), constitutional authority? Which subject actions were “official” (“at least presumptive immunity”) but not “conclusive and preclusive” constitutional? Different term, “official”, from conclusive and preclusive constitutional authority. What is the cash value of the distinction? One consequence would be that Jack Smith could rebut the “presumption”.  Which subject actions would be “unofficial” (“no immunity”) Some presidential actions, clearly, are not official since "not everything a President does is official"? Are any of the subject actions unofficial? Back to you, Judge Chutkan.

This is the first time that the Supreme Court has ever ruled on the subject of presidential immunity so, to me, they had to adopt some sliding scale rule to this case. This tripartite scale is a common thing that SCOTUS does. The irony is that it looks so much like Roe v Wade's three trimester rule. This immunity decision looks very much like Roe. There’s “first trimester”, “conclusive and preclusive constitutionality”, the actor, president, or woman in Roe, can do whatever (s)he wants. Second trimester, “official” acts, the state has an interest. Actor has “at least presumptive immunity”, but not absolute. Better be careful. “Third trimester”, “unofficial” acts, actor has no protection whatsoever. It's because of this familiar construct that I reacted that the decision was "reasonable".