Why Is Trump Declaring War On Amazon?

President Trump took to Twitter on Friday to say that the US Postal Service is undercharging Amazon, making the "Post Office dumber and poorer." Trump was referring to a deal that Amazon has with the USPS which allows the e-commerce giant to pay less to deliver packages than it would with other delivery services. Trump's backlash against Amazon could cause problems for cities offering the company major financial incentives to host HQ2.