CLYDE, Ohio—After the Trump administration announced new tariffs on imported washing machines in January, Marc Bitzer, the chief executive of Whirlpool Corp., celebrated his win over South Korean competitors LG Electronics Inc. and Samsung Electronics Co.

“This is, without any doubt, a positive catalyst for Whirlpool,” he said on an investor conference call.

Nearly six months later, the company’s share price is down 15%. One factor is a separate set of tariffs on steel and aluminum, imposed by the U.S. in March and later expanded, that helped drive up Whirlpool’s raw-materials costs. Net income, even with the added benefit of a lower tax bill, was down $64 million in the first quarter compared with a year earlier.

In his next call with investors, in April, Mr. Bitzer struck a cautious tone. “There continues to be uncertainty regarding potential future tariffs and trade actions,” he said. “We’ll continue to monitor, evaluate and take the right action for our business.”

Put into practice, tariffs are a complex economic weapon that can ricochet through an economy in ways even proponents don’t expect. That’s what happened with washing machines, which were among the first consumer products targeted by the Trump administration.