The AP had this - it's going viral.
Not a good time for more negatives for the “WON” -
Rats are racing for the rails
Well, the deal with those tapes, they caught Nixon himself making admissions. However, this email would be considered contemporary documentation, same kind of credibility that reporter's notes receive ... very good, high.
I think the WH will try to get out by saying, "See? He says he wasn't promised a job, we're innocent!" Unfortunately, the same kind of precision to the language of the law in question prevails, the promise isn't necessary in order to commit the felony, the offer alone is sufficient.