In Warwick, R.I., Chris Ciunci sold more than 800 shares of Nike. In Wichita, Kan., Ken Wagnon bought on the dips. Outside Denver, Doug Johnson checked his portfolio, then went back to researching family-vacation options.

President Trump’s sweeping tariff plans, their sudden pause and his escalating trade war with China have turned the market into a rollercoaster. During the past several days, U.S. stock markets lost a stunning $7.7 trillion, then climbed sharply before retreating again Thursday. A steep selloff of long-term Treasurys especially alarmed analysts and investors, because the government bonds have traditionally provided an investing haven in times of upheaval.