Sen. Lindsey Graham (R-SC) speaks to members of the media in the basement of the U.S. Capitol prior to a Senate Republican Policy Luncheon January 17, 2018 in Washington, DC.

WASHINGTON — Senator Lindsey Graham of South Carolina has been one of the biggest proponents of President Trump's crackdown on China, welcoming tariffs on Chinese imports while conceding that they will raise costs for American businesses and consumers.

"There is no way for us to address China without absorbing some pain here," Mr. Graham said in August.

But behind the scenes, Mr. Graham has been working to help chemical and textile companies in his home state avoid the pain of Mr. Trump's trade war. The senator has advocated on behalf of seven South Carolina companies that import products from China, writing letters urging the Trump administration to remove materials they rely on from a list of goods subject to Mr. Trump's tariffs.

Mr. Trump's tariffs, Mr. Graham told the administration, could "economically harm consumers and stifle economic growth in South Carolina."

The senator has written seven letters to the United States trade representative on behalf of companies seeking tariff relief — more than any other member of Congress has penned. Four of those seven received at least some of the relief they were seeking.

The jockeying to protect South Carolina companies highlights the tension inherent in Mr. Trump's trade war, which is aimed at punishing China with tariffs on $250 billion worth of goods but is hurting many American companies in the process. Businesses across the United States have grown by embracing the global economy — producing, selling and buying goods from countries across the world, including China. As Mr. Trump threatens to impose even more tariffs on Chinese imports, many companies are appealing to the administration for relief — creating winners and losers in the process.

Hundreds of American companies have urged the Trump administration to keep their products off the list of goods being taxed. Executives, trade groups and citizens have filed more than 6,000 comment letters with the United States trade representative. Companies have appeared at hearings in Washington, hired lobbyists and enlisted lawmakers to fight on their behalf. The lobbying has had an impact, with the trade representative removing products with an annual import value of about $7.4 billion from the list.

Among the companies appealing to the trade representative were seven firms with operations in South Carolina, including Mitsubishi Chemical America, Standard Textile and paper manufacturer Archroma.

In September, Mr. Graham wrote letters to Robert E. Lighthizer, the United States trade representative, on behalf of those firms, arguing that the tariffs would cause irreparable harm to domestic companies.

"China's behavior has unjustifiably burdened and restricted U.S. commerce and I am encouraged by President Trump's attention to this important issue," Mr. Graham wrote in each letter. "However, stiff competition from global competitors forces domestic manufacturers to absorb the additional cost of a tariff. This could put South Carolina companies at a competitive disadvantage."

Mr. Graham went on to urge "careful consideration" of a list of product codes that applied to each company, then said that imposing tariffs on them had "the potential to economically harm consumers and stifle economic growth in South Carolina." At the conclusion of each letter, he said that "I appreciate your attention to these constituent requests and your continued efforts to combat China's unfair trade practices."

Mr. Graham's efforts helped four of the seven companies. The final list of tariffs on $200 billion worth of goods dropped three lines of chemicals used by Mitsubishi Chemical America, a Japanese company with an office in Greer, S.C. It removed one line of fabrics imported by Archroma U.S., a chemical company with a plant in Marin, S.C., and two lines imported by Domtar, a paper manufacturer with headquarters in Fort Mill, S.C., and a pulp mill in Bennettsville, S.C.

Also dropped from the list were three lines that affect Standard Textile, which has a plant in Union County, S.C. In 2017, the United States imported about $30 million worth of those three fabrics, $25 million of which went to South Carolina, according to Census Bureau data.

The product lines that Mr. Graham specified — and were removed from the tariff list before it was finalized last month — account for more than $430 million of imports from China annually, according to federal data. That's about 6 percent of the total value of products removed from the final list.

"Only a fool would not know that Lindsey Graham fights tooth and nail for business in South Carolina," Kevin Bishop, a spokesman for Mr. Graham, said in a email. "He takes great pride in standing up for working men and women in our state, and that's never going to stop."

The United States trade representative officials did not respond to questions about whether Mr. Graham's efforts influenced their decisions on the final list.

The trade representative's records show that 40 members of Congress submitted formal comments over the proposed list of products for the most recent round of tariffs, which begin at 10 percent on $200 billion of imports, and are set to escalate to 25 percent next year. Most filed only one comment. None filed more than three, other than Mr. Graham.

Representative Emmanuel Cleaver, Democrat of Missouri and a critic of Mr. Trump's China tariffs, wrote three letters urging changes to the most recent tariff list, including the removal of gift bags imported by Hallmark and cement products imported by Demdaco, a home décor company. Mr. Cleaver also asked the administration to include on the list a category of products that includes imported log splitters, which compete with splitters made by Blount International, which has a factory in Kansas City.

Other Republican senators who sought changes to the tariff list include Ron Johnson of Wisconsin, who joined a bipartisan letter on behalf of paper manufacturer Appvion; Jerry Moran and Pat Roberts of Kansas, who jointly advocated on behalf of Pitsco, a small Kansas company that sells model car kits and other materials for science and math education; and Roger Wicker of Mississippi, who expressed concern that any additional tariffs could hurt United Furniture Industries, a manufacturer headquartered in Tupelo, Miss.

Alaska's entire Republican delegation — Senators Lisa Murkowski and Dan Sullivan, and Representative Don Young — wrote Mr. Trump in August, asking that he remove tariffs on fish caught in Alaska but processed in China. The administration eventually spared some lines of processed seafood from its final list of tariffs, including some Alaska-caught fish.

Senator Rob Portman of Ohio, a former trade representative under President George W. Bush, sent a letter containing dozens of product codes that he said were drawn from "Ohio constituent entities that have weighed in with my office."

Mr. Portman has said that a tariff escalation with China "is not good for us," but he has praised the administration for taking a hard line against Chinese trading practices. His letter asked that some of the product codes be added to the list and others subtracted.

Mr. Portman did not name the companies, nor warn of any economic damage if his recommendations were not heeded. Twenty-five of the product lines that he requested be dropped were removed from the final list. Some of his suggestions overlapped with Mr. Graham's, including the textile lines requested for removal by Standard Textile, which is headquartered in Cincinnati.

A critic of Mr. Trump when they were rivals for the Republican presidential nomination in the 2016 campaign, Mr. Graham has refashioned himself as one of the president's closest allies in the Senate, most recently with his impassioned defense of the president's Supreme Court nominee, Brett M. Kavanaugh, against allegations of sexual assault.

South Carolina's economy depends heavily on trade, but Mr. Graham has rarely wavered in his support for Mr. Trump's trade agenda — including the imposition of tariffs against China — in an effort to force Beijing to end a long list of trade practices that the administration says violate international rules.

"I'm very pleased and supportive of President Trump's efforts to push back against China's intellectual property theft, dumping, and other unfair trade practices," Mr. Graham said in a news release in March, when the president announced a first wave of tariffs on $50 billion in Chinese imports.

After Mr. Trump met in June with Republicans concerned over his trade policies, Mr. Graham released another statement.

"Now is not the time to undercut President Trump's ability to negotiate better trade deals," he said. "I will not support any efforts that weaken his position."

Mr. Graham's letters were shorter than most of his colleagues', and they were nearly identical to one another, changing only the names of the company in question and the product codes that affect it.

The companies Mr. Graham cited in his letters include multinationals that have set up operations in the United States. Archroma, which has a parent company headquartered in Switzerland, told administration officials in its own comment letter that tariffs on the chemicals it imports "will force Archroma to raise prices and customers will shift their purchases to foreign competition."

Mitsubishi Chemical America's president, Dennis Price, testified in August that tariffs on chemicals that are critical to its manufacturing of lithium ion batteries for electric cars would "force us to reconsider our investments in the United States and our plans to continue to grow our manufacturing footprint in this country."

One of the companies Mr. Graham advocated, Standard Textile, welcomed his efforts but a spokeswoman said it did not know if they had helped.

"Standard Textile and Senator Graham each filed comments with U.S.T.R. requesting that additional tariffs not be imposed on certain intermediate products imported by Standard Textile from China because these intermediate products are required to support manufacturing jobs in South Carolina," a spokeswoman for the company, Judy Sroufe, said in an email, referring to the trade representative. "Standard Textile has no visibility into whether or not Senator Graham's letter influenced the decision by U.S.T.R."