What’s the history of the Panama Canal, and why is Trump threatening to retake control of it?

President-elect Donald Trump over the weekend suggested the US should retake the Panama Canal, an idea that was immediately rejected by the government of Panama, which has controlled the passage for decades. In social media posts and remarks to supporters, Trump accused Panama of charging the US “exorbitant rates” to use the canal and hinted at growing Chinese influence over the crucial waterway.