It is questionable whether an NDA, outside of one for valid security matters, is even enforceable against a federal employee. I suspect we will have an answer to that by the time trump leaves office as he has claimed to be suing several former White House employees for violating an NDA.
Here is a news article about this specific issue.
https://www.google.com/amp/s/mobile..../idUSKBN1GV2UT

