https://www.frontpagemag.com/the-democrats-war-on-executive-privilege/
“Background on Executive Privilege”
“Executive privilege refers to a wide variety of evidentiary and substantive privileges. Despite its importance, executive privilege has never been conclusively defined by Congress or the executive branch. [Italics mine]. An executive order issued on November 1, 2001, however, catalogues the most important species of executive privilege claims:
The President’s constitutionally based privileges subsume privileges for records that reflect: [1] military, diplomatic, or national security secrets (the state secrets privilege); [2] communications of the President or his advisors (the presidential communications privilege); [3] legal advice or legal work (the attorney-client or attorney work product privileges); and [4] the deliberative processes of the President or his advisors.
The most extensive discussion of these varieties of executive privilege is found in federal case law. (When Congress and the executive have clashed over privilege issues, their resolutions of the conflicts have not yielded precise formulations. Congress tends to use blunt instruments, such as the purse power or confirmation authority, to extract concessions from the executive. The infrequent executive-legislative conflicts that have reached the courts ended inconclusively.”
The above memo shows that “executive privilege,” at least when it was written, was not narrowly or legalistically defined; and the term “advisors” was broadly defined. The Clintons, when I was a White House spouse, for instance, sought confidential advice from friends and supporters from many worlds; from Hollywood and Wall Street, from journalism to technology. The Presidency benefited from the President having a broad range of input in a confidential context.