John Kerry and North Vietnam.
My first thought. John Kerry never even pretended to speak for the United States Government. If Trump called Netanyahu offering more favorable treatment, or worse, or the same, when "he's in office" it would be a crime. It would be a crime for Trump to make representations about the policy of a future administration, unless he were elected, since it would give Israel an incentive to attempt to influence the election. He could be selling his office for foreign support for his election.
don’t forget Dennis Rodman and Lil Kim re: Kenneth Bae “I’m calling on the Supreme Leader of North Korea, or as I call him ‘Kim” to do me a solid and cut Kenneth Bae loose” - “told Obama to call Kim”
https://www.youtube.com/watch?v=ZmSqohnP3K4