A non-US ship can go to PR and then another US port. From the article:
"The concrete results are that a foreign ship can enter a U.S. port to drop off its foreign cargo, it can even from there sail to different U.S. ports to drop off other foreign goods, but it is not allowed to pick up any domestic goods in a U.S. port and bring those goods to another U.S. destination if it doesn’t meet the four conditions listed above."
"The concrete results are that a foreign ship can enter a U.S. port to drop off its foreign cargo, it can even from there sail to different U.S. ports to drop off other foreign goods, but it is not allowed to pick up any domestic goods in a U.S. port and bring those goods to another U.S. destination if it doesn’t meet the four conditions listed above."