HUGER, S.C. — Safely stationed in the control pulpit, Chris St. Amand is watching the pot boil.

Working the day shift at the sprawling Nucor Steel plant along the Cooper River here, Mr. St. Amand monitors a four-foot-wide lasagna noodle of steel as it is dunked into a molten broth of protective shimmering zinc.

He tracks every step of this galvanization process — from the caldron’s 865-degree temperature to the line speed — on a bank of flashing screens. Except, that is, for the screen at the bottom right. “I watch our stock and the Dow Jones on that one,” he said.

Mr. St. Amand, whose pay package includes profit-sharing, likes what he sees. Since Election Day, Nucor is up 13 percent.

Across the steel industry, stock prices — and spirits — have been on the rise, lifted by President Trump’s vow to protect American manufacturers against cheaper imports and invest as much as $1 trillion in infrastructure over the next decade.

“If you could design a perfect administration from the perspective of the steel industry, this would be it,” said Thomas Gibson, president of the American Iron and Steel Institute, ticking off the president’s promises to hack away regulations and lower taxes, while fending off foreign competitors and embarking on a “Buy America” building program.

Even before a single presidential vote was cast, American steel makers had been buoyed last year by record automotive sales and a series of penalties slapped on foreign producers like China for illegally dumping subsidized steel in the United States. “We expect our sheet and plate steel mills will benefit from trade actions taken over the last year,” said John Ferriola, Nucor’s chief executive.

Mr. Ferriola, one of the business leaders who met with Mr. Trump at the White House in February to discuss American manufacturing, is looking for further improvements. “We believe our full year 2017 could significantly exceed the level achieved for 2016,” he said, noting that “imports and inventories are down.”

Through the years, American producers’ main grievance has been that China treats its highly subsidized steel industry as a giant government jobs programs. The plants are paid to churn out steel — regardless of demand. The result is excess capacity, some of which China tries to ease by selling steel on the world market at Groupon-like discount prices.

Last month, Mr. Trump reaffirmed his resolve to crack down on dumping and investigate whether foreign-made steel endangered United States security. He also championed the use of domestic steel, promising to pursue an infrastructure plan under which “new ships, bridges, tunnels and airplanes will be constructed with American hands, American steel and, yes, American tools.”

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.

“It’s hot; it’s dirty. It’s hard work,” said Leigh Kemp, 48, who switched from an office job to the plant floor tending a ladle metallurgy furnace two decades ago. “But you make good money.”

The plant employs 940 workers, yet most of the acreage is occupied by highly automated machinery rather than people.