Economics textbooks insist that stock prices reflect the future stream of a company’s profits on any given day. For all the brainpower devoted to these forecasts, however, they are essentially rough estimates of what may happen over the next twelve months and wild guesses about anything after that.

President Donald Trump‘s wide-ranging tariffs went into effect Thursday, just as the economic fallout of the president's months-long tariff threats creates visible damage to the U.S. economy.