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.

In recent days the president-elect has called for asserting U.S. control over the Panama Canal and Greenland, showing that his “America First” philosophy has an expansionist dimension.

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.