Well just look at the narrative he's laying out. It's the archetypal leftist demagoguery. Big bad corporation gets richer off of hard working taxpayers, nyaahhhh.

Amazon doesn't tell the post office what to charge. Amazon doesn't make the post office lose money. Amazon is just participating in a free market and making the most advantageous decision it could.

Apparently this is a problem for Trump. But when Trump paid little or no tax using legal methods, he was a genius. WTF?

There's no way Trump is dumb enough to believe what he's saying. He knows Amazon hasn't done anything wrong. He has to know that the Post Office is a completely retarded enterprise. The rebuttal in that article was that "such and such finance guru says this contract is profitable". There's not a financial analyst with an IQ over 60 that believes that. This contract is indeed unprofitable, but so are ALL the contracts, not just Amazon.

He's picking on Amazon because A) He hates Jeff Bezos and B) he can satisfy his left-wing social ideology and engage in what is essentially a redistribution play. And C) He can tout the additional post office revenue as a victory and validation for his 'run-govt-like-a-business' schtick.