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.”