HENDERSONVILLE, N.C. — Rick Griswold, a 74-year-old lifelong Republican, doesn’t know much about Ted Budd, the congressman he plans to support on Tuesday in the party’s Senate primary election. But he knows exactly why he’ll cast his ballot for Mr. Budd.
“Trump endorsed him,” Mr. Griswold, an Army veteran, said as he collected tools at his part-time job at O’Reilly Auto Parts. “I like Trump.”
The former president’s branded “complete and total endorsement” doesn’t guarantee victory in a Republican primary. However, operatives working in Senate campaigns this year said that playing up Donald J. Trump’s imprimatur is the single most effective message in intraparty battles.
In North Carolina, Mr. Budd is proving the potency of pairing the former president’s endorsement with another from one of Mr. Trump’s on-again, off-again allies: the Club for Growth, an influential anti-tax group that has spent $32 million on federal races this year.
That amount is twice as much as that by any other outside group — and much of that spending has been against candidates Mr. Trump has endorsed, according to campaign finance data compiled by Open Secrets.
Mr. Trump has been furious about the Club for Growth’s campaigning against his picks. During a heated battle in the Ohio Senate primary, the group aired a TV spot of Mr. Trump’s choice in that race, J.D. Vance, criticizing the former president. Mr. Trump ordered an aide to text the group’s president, David McIntosh, telling him off in a vulgar message.
Mr. McIntosh, meanwhile, has said privately that he hoped the group’s recent endorsement of Kathy Barnette in Pennsylvania would help exact some revenge on Mr. Trump, according to people with knowledge of the conversations.
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Joe Kildea, a Club for Growth spokesman, said that “David has never expressed these sentiments.” “The only reason Club for Growth PAC endorsed is because Barnette is the only real conservative in the race,” Mr. Kildea said.
But in North Carolina, Mr. Budd was battling former Gov. Pat McCrory and former Representative Mark Walker after Mr. Trump announced his endorsement in June. Mr. Budd appeared to separate from the pack, helped by an $11 million advertising campaign from the Club for Growth mostly revolving around the former president’s endorsement. The group’s most-watched TV spot of the race was footage of Mr. Trump’s announcement of his endorsement of Mr. Budd.
Last week, Mr. Budd was 27 percentage points ahead of the rest of the field, according to a poll from Emerson College, The Hill and WNCN-TV, the CBS affiliate in the Research Triangle of North Carolina. The Club for Growth has also curtailed its spending on the race, signaling its calculation that Mr. Budd is safely ahead.
The winner of the state’s Republican Senate primary will head into the November general election with a distinct advantage over the Democratic nominee, who polls indicate will be Cheri Beasley, a former State Supreme Court justice. Republicans have won the last four North Carolina Senate races and the past three presidential contests in the state.
Doug Heye, a Republican who has worked on three North Carolina Senate campaigns, said Mr. Budd was a strong but relatively unknown candidate across the state. His rise, Mr. Heye noted, showed the power of a well-funded, Trump-endorsed primary campaign.
“It’s not surprising Budd is emerging,” he said. “But these margins look pretty big, especially considering he’s running against a former governor and a former congressman.”
Mr. McCrory disputed the polling and criticized the Club for Growth, a 23-year-old conservative outfit he described as a political gun-for-hire that had strayed from its original mission of promoting low-tax, limited-government policy.
“The Club for Growth is trying to buy the North Carolina Senate race,” Mr. McCrory said. “And we’re trying to do everything we can to stop them.”
Mr. Budd, 50, promoted himself as a gun shop owner during his first congressional campaign in 2016. He had been involved in several businesses after divesting in 2003 from the Budd Group, a company started by his father that provides janitorial, landscaping and other corporate facility maintenance, a spokesman said.
This year, Mr. Budd has mostly kept his head down. He has visited all 100 counties during the campaign, which his team said was a factor behind Mr. Budd’s skipping all four Republican primary debates.
“We’ve been focused on the fundamentals, like getting organized in all 100 counties,” said Jonathan Felts, a senior adviser to Mr. Budd.
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Mr. Budd compiled a staunchly conservative voting record during his six years in the House, one that aligned closely with both Mr. Trump and the Club for Growth.
He voted to overturn presidential election results after a mob of Trump supporters rioted in the Capitol on Jan. 6, 2021, and signed a letter in the days after the election urging the Justice Department to investigate voter fraud and irregularities.
In text messages after the election that were obtained by CNN, Mr. Budd inaccurately suggested to Mark Meadows, then the White House chief of staff, that Dominion Voting Systems might have had a connection to the liberal billionaire George Soros, a bogus claim pushed by multiple Trump allies.
After the Club for Growth opposed Mr. Trump during the 2016 Republican primary race, the two sides patched up the relationship. But in primary campaigns this year, they are not always aligned. In Ohio, the group spent $8 million for Josh Mandel, while Mr. Trump backed the eventual winner, Mr. Vance.
In the Pennsylvania Senate primary on Tuesday, Mr. Trump supports Dr. Mehmet Oz, the longtime television personality. Meanwhile, the Club for Growth endorsed Ms. Barnette, a conservative author and political commentator who has surged in the polls. In the Alabama Senate contest next week, Mr. Trump rescinded his endorsement for Representative Mo Brooks, while the Club for Growth has stood by him.
Still, the Club for Growth and Mr. Trump were on the same side in a contested West Virginia House primary this month. In that race, their support for Representative Alex Mooney helped him coast to an 18-point victory over his House colleague David McKinley, who had support from much of the state’s political establishment. The Club for Growth spent more than $1 million in that House race, twice as much as any other outside group.
With two more weeks remaining in the first full month of primary contests this year, the Club for Growth super PAC has already spent $32 million on federal races. That’s twice as much as any other outside group and already half of what the group spent in the 2020 election cycle. In recent years, much of the super PAC’s funding has come from Uline Inc., a shipping company owned by Dick and Liz Uihlein, and Susquehanna International Group, an investment company co-founded by Jeff Yass.
In 2016, the Club for Growth endorsed Mr. Budd and spent $500,000 to help him emerge from a crowded primary. The Budd family later donated at least $50,000 to the group.
This year, the group has spent $11 million supporting Mr. Budd, roughly 57 percent of the outside spending in the Republican Senate primary.
Heading out of her local polling place during early voting on Thursday, Cyndi Glass, 63, said she was aware of just two Senate Republican candidates. One was Mr. McCrory, but she said she “wanted something different.”
The other was Mr. Budd.
“Trump endorsed him,” she said. “And that was a plus for me.”