Amid the continuing tariff threats, both LG and Samsung decided to build washer plants in the U.S. LG’s plant in Clarksville, Tenn., is slated to open in the fourth quarter and initially employ about 600 workers. “My mandate is to get it done as soon as possible,” said Paul Bradford, who is overseeing construction.

An LG spokesman said the manufacturer began exploring a possible U.S. factory in 2010 and that the tariff threat spurred the company to speed up construction. A USTR official said the tariffs encouraged both firms to move ahead with their U.S. production plans.

Samsung started producing washers in January at a retrofitted plant formerly run by Caterpillar Inc. in South Carolina. With more than 600 workers, it was churning out more than 1,000 washers a day as of this spring, said Tony Fraley, who oversaw the factory’s rapid renovation for Samsung before leaving the company. Samsung didn’t respond to a request for comment about the production rate.

People familiar with the matter said Mr. Trump’s election influenced Samsung’s decision to produce in South Carolina.

Samsung said it hired many laid-off former Caterpillar workers. The unemployment rate in Newberry County, the site of the plant, dropped to 2.6% in May from 3.5% in the same month a year earlier. Foster Senn, mayor of the city of Newberry, said developers are contemplating building a new hotel and subdivision.

In Clyde, some employees at Whirlpool and one nearby supplier said the tariffs are working. “If not for that, Whirlpool wouldn’t have been able to hire,” said Matthew Morton, 42, who works for a supplier and has a son who works at the washer factory.

Some Whirlpool workers said recent production stoppages have fueled questions about the outlook. “Everything is now thrown back into a flux,” said Mr. Black, the mayor, himself a former Whirlpool employee. His wife, children and other relatives work at the plant. “People’s anxiety level is higher because nobody knows what’s going on.”