U.S. stocks suffered their worst week in more than two years, signaling mounting investor anxiety over whether factors from restrictive trade policies to rising interest rates could disrupt the nine-year bull market.

The Dow Jones Industrial Average fell more than 1,400 points over five days, a 5.7% decline that marked the blue-chip index’s biggest weekly percentage loss since January 2016. Financial stocks in the S&P 500 dropped 3% Friday, with Bank of America and Morgan Stanley falling nearly 5% apiece. Tech stocks...