This looks new to me. It becomes hard for prosecutors to prove anything when we can’t ask about motives and the witnesses are ‘privileged advisors’. From the officical court opinion – note it is in paper-format with hyphens. (page 18: https://www.supremecourt.gov/opinions/23pdf/23-939_e2pg.pdf):
In dividing official from unofficial conduct, courts may not inquire into the President’s motives. Such an inquiry would risk exposing even the most obvious instances of of- ficial conduct to judicial examination on the mere allegation of improper purpose, thereby intruding on the Article II in- terests that immunity seeks to protect. Indeed, “[i]t would seriously cripple the proper and effective administration of public affairs as entrusted to the executive branch of the government” if “[i]n exercising the functions of his office,” the President was “under an apprehension that the motives that control his official conduct may, at any time, become the subject of inquiry.”
(page 31)
The indictment’s allegations that Trump attempted to pressure the Vice President to take particular acts in connection with his role at the certification pro- ceeding thus involve official conduct, and Trump is at least presump- tively immune from prosecution for such conduct.
No. You plead the 5th once you are in court. This says that when Nixon wanted the FBI to stop investigating the Watergate break-in, we couldn’t ask why because the prez is supposed to talk to the FBI and we can’t question his motives. It says that when Trump asked Pence to hold the vote and bring in fake electors, it was official communication and therefore legal – because we can’t ask why. It says that when Trump wanted false charges of fraud brought up for elections, saying his lawyers would figure out the reasons later, that was OK because he’s officially supposed to investigate fraud. Prior to this, any potential overlap between the Office of President and potential Candidate for Presidency (and/or candidate for future jail term) could be investigated as if it was not Presidential until there was a solid defense as to why it was official. The ruling turns that on its head and says prosecution must first find proof that actions were unofficial – and do so without the ability to ask about motivations – before filing charges. We want the official/unofficial decision to be made with the weight of context and done in court rather than putting prosecutors in the position of ‘illegally’ investigating a President before they can figure out what actually went down.