When Representative Ralph Norman addressed about 250 supporters munching on Chick-fil-A chicken nuggets in a civic center in Anderson, S.C., on Friday night, he was quick to acknowledge the biggest obstacle to his bid to become the next Republican senator from South Carolina.

“Who said Donald Trump was the only one who can get a crowd?” Mr. Norman joked, a reference to the thousands of people who had gathered clear across the state on the South Carolina coast, where Mr. Trump was using the power of his presidency and his considerable political muscle to boost Senator Darline Graham for the job the congressman was seeking.

Republicans in the state will vote on Tuesday in a special runoff election to replace former Senator Lindsey Graham, Ms. Graham’s brother who died last month, on the ballot in November. And Mr. Norman, a hard-line conservative who has staunchly backed Mr. Trump’s agenda over his nine years in Congress but sometimes clashed with him on spending, is hoping that voters will reward his record — contrarian streak and all — and reject the president’s efforts to anoint a senator.

“I mean, the president, he’s an asset wherever he goes — he draws a great crowd,” Mr. Norman said in an interview. “Would I have liked his endorsement? Yeah, I would. But we didn’t, and that’s fine. The people in South Carolina are going to pick their next senator, though.”

In the critical final days of the abbreviated race, Mr. Norman has found reasons to believe it may be him. There are signs that Mr. Trump is no longer the Republican kingmaker he once was, including in South Carolina, where voters rejected his preferred candidate in the governor’s race. Mr. Norman, who ran unsuccessfully in that election, is hoping that voters spurn Ms. Graham — whose flub at a televised debate last week highlighted her inexperience — in favor of someone more seasoned.

“My record is my biggest asset,” he said. “I’m a known quantity.”

The silver-haired Mr. Norman, 73, is in many ways a product of South Carolina’s defiant and idiosyncratic political tradition. Like Mr. Trump, he is a wealthy businessman who ran his family’s real estate firm before entering politics. Over two decades, he has vocally denounced what he calls a broken Washington establishment. Mr. Norman strongly supports the president’s immigration crackdown and his demands to end the filibuster to enact voting restrictions.

But in the president’s estimation, he has two major flaws. Mr. Norman did not initially endorse Mr. Trump in his presidential bid in 2024, instead backing Nikki Haley, the former South Carolina governor and a longtime friend of his.

And Mr. Norman has styled himself as a fiscal hawk, aligning with a group of ultraconservative Republicans whose hostility to government spending has put them at odds with the president and party leaders at key moments.

Mr. Norman has used his position on two influential House committees to hold up Republican legislation, including Mr. Trump’s signature domestic policy law, in a bid to slash costly provisions. He twice opposed candidates for House speaker backed by the president, forcing Mr. Trump to call and pressure him.

More often than not, Mr. Norman will fall in line. But his recalcitrant posture may have widened the rift that cleared the way for Mr. Trump’s endorsement of Ms. Graham, who had never held public office before being appointed last month to her brother’s seat after his death.

Ms. Graham and her allies have seized on Mr. Norman’s clashes with Republican leaders to portray him as a rabble-rouser who is insufficiently loyal to Mr. Trump.

“It would be better to have a seat at the table than to be forced there in a high chair,” said State Senator Josh Kimbrell, who is backing Ms. Graham. “And I think what Ralph’s done over the years is he played the contrarian because he thinks that does well on Twitter.”

When he entered Congress in 2017, Mr. Norman quickly took up with the House Freedom Caucus, a group of right-wing Republicans who are among Mr. Trump’s most vocal backers but frequently clash with their party on spending issues.

Mr. Norman is one of several holdouts who have threatened to derail Republican bills to seek concessions, only to ultimately capitulate with or without them.

Mr. Norman insists that his objections are necessary to keep Republicans committed to fiscal discipline. Last year, he and several other lawmakers on the House Budget Committee held up their party’s sweeping tax cut and domestic policy bill to secure deeper cuts to clean energy tax credits enacted by Democrats.

Mr. Norman said that Mr. Trump, who campaigned on repudiating those credits, backed that effort.

“Ralph wants to work to get to yes,” said Representative Chip Roy, a Texas Republican who is a close ally. “But Ralph isn’t going to be sold a bad deal, and all of these establishment hacks in Washington want you to accept a bad deal for political expediency.”

Still, facing significant pressure, Mr. Norman relented on other demands. And despite estimates that the Republican domestic policy bill would add trillions of dollars to the national debt, Mr. Norman ultimately voted for it.

“I bet Ralph was somewhat surprised that Trump got involved against him,” said Representative Thomas Massie of Kentucky, one of two Republicans to vote against the legislation. “Because he’s been a completely reliable vote for Trump.”

Mr. Norman entered politics in 2004, when he won an election to serve in South Carolina’s House of Representatives. Though he gave the seat up to mount a losing bid for Congress in 2006, he returned to the state legislature in 2009, running as a fiscal conservative at a time when the Tea Party movement was boosting such candidates across the country.

Mr. Norman was elected to Congress in a special election in 2017. A reliable ally of Mr. Trump, he backed the president’s efforts to reject the results of the 2020 election. In a misspelled text in 2021, he asked the White House chief of staff to urge the president to invoke “Marshall law” to stop Joseph R. Biden Jr. from taking office days before his inauguration.

The congressman’s profile grew after Republicans narrowly won the majority in the 2022 midterm elections. In the time since, Mr. Norman has at points refused to back both Republican speakers. He has held up spending and defense bills, voted against a deal to suspend the federal debt ceiling and forced Speaker Mike Johnson to win support from Democrats to help push through a foreign aid package.

Some of his supporters regard such rebellions as Mr. Norman’s biggest selling point.

Tara Servatius, a conservative talk radio host in South Carolina, commended Mr. Norman “for having the guts to stand up to Kevin McCarthy, Joe Biden and occasionally Donald Trump when he spent a little too much money.”

Mr. Norman has avoided directly criticizing the president during his campaign. During last week’s debate, he said that Mr. Trump needed to end the war in Iran swiftly but clarified that he simply wanted the president to explain his strategy. And he has not attacked the president for endorsing Ms. Graham.

“I don’t understand it, but that’s his prerogative,” Mr. Norman said on Friday. “I don’t blame him for that. And what he’s done for the country is fantastic.”

But Ms. Graham has argued that Mr. Norman cannot be relied on, in part citing his decision to back the presidential bid of Ms. Haley, who lost her home state by more than 20 percentage points.

“He didn’t support President Trump; he supported Nikki Haley,” Ms. Graham said in an interview on Thursday at a bar in Boiling Springs, S.C. “And when it came to the big, beautiful bill, he was the one holdout that had to be convinced to vote for it. So that’s why I question his commitment.”

Ms. Graham quickly won the backing of Mr. Trump, who was close to her brother. She has endorsements from South Carolina’s governor and Senate Republican leaders, and she has support from their campaign arm. She has also benefited from millions in spending from super PACs that were once backing her brother’s bid.

Ms. Graham has drawn support from an outside group backed by the renewable energy industry, the Invest in Tomorrow Coalition, which has spent $1 million in attack ads against Mr. Norman over his effort to gut the clean energy credits.

Mr. Norman has largely self-funded his campaign, and he has pointed to the outside spending as evidence that Ms. Graham is being propped up by Washington elites.

“She’s unknown, but she’s been backed by a group that is known, and it’s not South Carolina values,” he said. “The millions they’re putting in to totally destroy me — I don’t care.”

On Friday, he won the endorsement of Mark Sanford, the former South Carolina governor who finished fourth in the primary.

Mr. Sanford, who once brought live pigs onto the statehouse floor to protest government spending, cited Mr. Norman’s fiscal conservatism and his experience. He said that he was particularly concerned about the growing national debt, which topped $40 trillion last week.

“It has heinous implications for all of us,” Mr. Sanford said. “And so, as much as I would like to honor tradition and old friendships, the stakes are simply too high as our nation really is at a financial tipping point.”

Catie Edmondson contributed reporting from Washington.