Via The Daily Beast:

After much controversy, President Trump on Thursday morning finally authorized that a century-old shipping law be waived in order to expedite the delivery of critical supplies to Puerto Rico. The Jones Act requires that all goods shipped between U.S. ports must be carried on ships built, owned, and operated by Americans. Trump initially expressed hesitance to waive the rule, “We have a lot of shippers and a lot of people that work in the shipping industry that don’t want the Jones Act lifted.”

There was an enormous public pressure campaign, led by Sen. John McCain, to waive the restrictions that were crippling relief efforts. (Trump waived it for the states affected by hurricanes Irma and Harvey.)