A Panamanian national holiday remembering the killing of 21 protesters by police and U.S. troops in 1964 is taking on new resonance this year as U.S. President-elect Donald Trump threatens to take back control of the Panama Canal.

There were many reasons that Ronald Reagan defeated Jimmy Carter in 1980. The Panama Canal Treaty wasn’t among them.

If commercial fees are typically low and America’s navy already has cheap and preferential access, why is Mr Trump threatening to take the canal? The simplest answer may be that the president-elect is expressing geopolitical machismo,