In many places, politicians (ie public figures) have less rights concerning such things than private people. (https://en.wikipedia.org/wiki/Defamation#Public_figure_doctr...)

At the point when Gizmodo published the memo and later the New York Times, Damore was not a public figure. He became a public figure because of the media attention. As such those media networks would likely not be able to use the public figure defense in this case, but they can use the public figure defense in regard to Obama.

To make a similar parallel, political satire is legal but if you do the exact same to a private person it would be harassment. The difference between the two is that one target a human being with the intent of doing personal harm, and the other targets a political role with the intent of creating discussion.