Like many of you, I’ve been going over Chief Justice John Roberts’ presidential immunity decision, trying to understand the distinction it sets out between “official” acts of a president, which are immune from prosecution, and “unofficial” acts, which are not immune. And I wanted to share with you a particularly troubling aspect. Having served in the Justice Department soon after Richard Nixon sought to use the department to go after the people on his “enemies list,” I was struck by Roberts’s assertion that a “president may discuss potential investigations and prosecutions with his Attorney Ge…