“We are America’s mistress,” a streetcorner philosopher told me during my recent visit to Panama. “One day Mr. Trump looked down at us and said, ‘Hey, you have another boyfriend—and he’s Chinese! Get rid of him!’ So we dumped the Chinese guy. We had no choice. That’s what it means to be Panama.” Last year, under pressure from Washington, Panama abruptly terminated a contract under which a China-based company ran ports at both ends of the Panama …