Well, for example, he could start appointing lackeys to the USPS governing board, who would presumably appoint a new Postmaster General more in line with his views. Those views could include making life very hard for Amazon (who, judging by the delivery method of my packages, still do quite a lot of business via USPS).
Just an anecdote- my postal carrier is a contractor for the USPS. She is terminating her contract early because the USPS has tripled the number of packages she has to deliver with no increase in pay.
My neighbors are all up in arms over this. They blame Amazon entirely for this woman’s troubles. On our FB group they’re talking about boycotting Amazon entirely.
Personally, I think both the USPS and the carrier negotiated their contracts poorly.
Mr. Trump has the power to do this. And he did, just a few weeks ago. Mr. Trump is realizing the extent of his powers and is beginning to use the office of the Presidency with efficacy.
The tariffs did not increase the price of steel by 25%, they added a 25% tariff to imported steel. The US imports under 1/3rd of the steel we use (36M mt vs 81M mt), so the majority of our steel will have no tariffs on it.
Like, say, directing the Justice Department to launch antitrust proceedings against Amazon.
I'm not saying that the Justice Department would take the case to court (still less that they would win). But the stock market may care about such possibilities, because if they happened, Amazon's share price would take a hit - a bigger hit than it takes just from Trump whining about them.
