Listen to the podcast segment "Don't let the President wage war on Amazon" from the May 19, 2018 episode
President Trump wants the US Postal Service to punish Amazon: This cannot be viewed apart from an apparent vendetta against Jeff Bezos, who started Amazon and who (separately) owns the Washington Post (which isn't gentle to the President, nor should it be).
The President does not deserve credit for reportedly donating his government salary if he is simultaneously using the government to advance his own personal business agenda or to punish others for behavior he doesn't like. It's not consistent.
This kind of abuse of power is intolerable, and it doesn't matter who's in the White House or what policies they otherwise claim to support. Abusing power is not acceptable, ever.