> I think the implicit argument is that he wants to avoid more canceled contracts, along with other forms of retribution like personal attacks he experienced a few years earlier.

That makes no sense at all. If the primary concern was avoiding canceled contracts, it would be in his best interests to ensure that the guy who is threatening to cancel contracts out of spite would not be elected.

Pressuring the Washington Post to not endorse the candidate who does not pose that threat goes exactly against that.

It's something else.