The Ford pardon of Nixon would have been totally unnecessary. A million other actions and arguments in American history assume presidents aren't immune. It's a totally new idea, nowhere in text or American tradition. Arguably the least originalist major SCOTUS decision in American history.
"The President wants me to argue that he is as powerful a monarch as Louis XIV, only four years at a time, and is not subject to the processes of any court in the land except the court of impeachment."
Roberts: "This also means he's allowed to use his power to get around that four years thing"