Now, he's demanding an audit of the Postal Service's finances. Trump didn't say he's specifically looking into the Post Office's deal with Amazon, but it seems like he's trying to back up his claims.
One of his main contentions is that Amazon is ripping off the U.S. Postal Service, but it's not clear whether it is getting the short end of the stick from the Jeff Bezos-led retailing juggernaut.
In fact, Amazon may be saving the post office from financial ruin.
It's true that the post office is losing money. It reported a $2.7 billion net loss in 2017.
But the post office is not funded by U.S. tax dollars.
And when you look at the revenue breakdown, you can see that shipping and packages is actually one of the few categories that brought in more money than the previous year. While overall revenue fell $1.8 billion, shipping and packages saw a $2.1 billion increase in revenue. Meanwhile, first-class mail revenue was down around $1.8 billion.