The top American official (the position is called 'charge d'affaires') in China this week quit in protest of Trump's withdrawal from the Paris Climate Agreement.
Trump pulled out of the agreement, saying that the deal wasn't good for the U.S. relative to other participants who get more out of it and pay less. Obama originally entered the deal without bringing it before Congress. It was widely considered that it would not have passed Congress if he had done it that way.
David Rank served 27 years in the Foreign Service before quitting.