President Donald Trump has promised to create an age of American exceptionalism with policies that put the United States first and ahead of other nations. But Trump’s moves in the early days of his administration have had the opposite outcome for the U.S. stock market. The S&P 500, which for years had been soaring above the stock indexes of other countries, is now trailing major markets in Europe and China, as investors have started to pull money from the United States and reallocate it around the world. Since Trump’s inauguration, the S&P 500 has fallen 6%, while the Dax index...