Mr. Trump’s attention to trade and manufacturing — which helped him gain the White House — means more here than any of the stumbles and missteps that feed late-night television comics. At this Berkeley County mill, neither the administration’s backtracking on a promise to use American-made steel in the Keystone XL Pipeline or its messy battles with congressional Republicans and low approval ratings have damped optimism about the president or his agenda.

“My confidence hasn’t been shaken at all,” said Mr. St. Amand, 37, who moved from Kentucky 16 years ago to take an entry-level job at Nucor as a packager. “Trump is good for business,” he said, repeating a sentiment expressed by 20 other employees interviewed — including a handful who voted for his opponent. (Mr. Trump won 56 percent of the county’s votes, to Hillary Clinton’s 39 percent.)

Jeffrey Goude, 29, nicknamed Strawberry for the curly red beard and hair that peeks out of his green hard hat, agreed. “All of them get criticism,” he said of politicians. “Trump is No. 1 for this industry. He’s trying to make America great again.”

That phrase not only echoes Mr. Trump’s campaign slogan, but also the title of a 2015 book by Nucor’s former chief executive, Dan DiMicco, who was a senior economic adviser during the campaign and a member of the president’s trade transition team. In the book, “American Made: Why Making Things Will Return Us to Greatness,” Mr. DiMicco argues that trade policies and the reluctance to impose punishing tariffs have cost the United States millions of manufacturing jobs.

With more than 200 facilities and $16 billion in sales last year, Nucor is well positioned to take advantage of an upswing in domestic demand. The company uses advanced technology to turn scrap metal into skyscraper-worthy support beams, paper-thin water heater linings and delicate sheets that can be molded into Christmas ornaments and fishing lures.

“We’re very flexible,” said Giff Daughtridge, the Huger plant’s general manager and vice president. “We can take cold scrap and turn it into product very quickly.”

The fiery showers of orange sparks, mammoth tipping buckets and pounding rollers are roaring round the clock here, staffed by four rotating teams that work 12-hour shifts.