A year and a half into Donald Trump’s presidency, Henry Kissinger set out a theory. “I think Trump may be one of those figures in history who appears from time to time to mark the end of an era and to force it to give up its old pretences,” he told the Financial Times. “It doesn’t necessarily mean that he knows this, or that he is considering any great alternative. It could just be an accident.” A term has been coined to describe this notion: Ryan Evans of War on the Rocks calls them “Trumportunities.” It is the idea that,...