It's unclear how the issue of ownership of the Panama Canal became a talking point for President-elect Donald Trump this week, but the question has a long political history.

President-elect Donald Trump spent Christmas Day laying out his foreign policy aspirations for his second term, including his threat to retake control of the Panama Canal. He also suggested the U.S. could take control of Greenland and Canada.

Trump again having designs on Greenland comes after the president-elect suggested over the weekend that the U.S. could retake control of the Panama Canal if something isn't done to ease rising shipping costs required for using the waterway linking the Atlantic and Pacific oceans.