It's not be just because of the Washington Post, although that is certainly a contributing factor. There is also reason to believe that Trump wants to go after

It's not be just because of the Washington Post, although that is certainly a contributing factor. There is also reason to believe that Trump wants to go after Amazon because Amazon is hurting brick and mortar retail, which also hurts commercial real estate, which also hurts him financially. Also Jeff Bezos is very wealthy, and Trump might view him as a rival. I am not a Trump supporter, however it may be true that Amazon is in fact underpaying taxes. What's repugnant is that I don't believe Trump's motivation is about making sure everyone pays their fair share into the system. It's more just transparent resentment, as well as a tactic to go after rivals.