As an effort to help domestic producers, the tariffs worked — very briefly. Whirlpool added 200 jobs at its factory in Clyde, Ohio. Its stock price jumped $20 per share in the first few days after the tariffs took effect.

Then things went bad.

A year after Mr. Trump announced the tariffs, washing machine prices were up, as many analysts had expected. But that has not been a boon to the makers of washers because fewer Americans are investing in new laundry equipment, exposing how protectionist trade policies can backfire on the very companies they are meant to safeguard.