Specifically, the S&P 500 declined 19.8% over a three-month period between September and December 2018, but the index had recouped its losses and reached a new high by May 2019. That's because the market tends to overreact to good and bad news.

Down nearly 40% since inauguration, Tesla stock has become the face of the tariff-spurred stock market selloff.

Stocks are falling again on Wall Street as companies and investors react to President Donald Trump’s decision to impose tariffs on the U.S.’s biggest trading partners. The S&P 500 dropped 0.7% Tuesday morning,