Even as Trump’s Standing Slips, He Slingshots Darline Graham to Victory

President Trump had seemed to be in danger of taking a major defeat on Tuesday night.

His choice for Senate in South Carolina, Darline Graham, had admitted at a debate that she wasn’t “that informed on national security.” Mr. Trump’s so-far-stingy super PAC was forced to spend more than $800,000 to help her. Many South Carolina Republicans expected her to lose, in what would have been the president’s first defeat in a Senate primary all year.

Instead, as Mr. Trump has done often since his rise to power a decade ago, he defied electoral expectations.

Ms. Graham’s narrow primary runoff victory on Tuesday night in the race to succeed her brother, the late Senator Lindsey Graham, was a show of force by a president who invested significant political and financial capital to ***ist her quest. His efforts ensured that Ms. Graham, who had no political experience to speak of and was little known before her brother’s death last month, will now be favored to serve in the Senate through at least 2032.

The outcome in South Carolina, one of the final major primaries before the midterm elections in November, offered a reminder of Mr. Trump’s influence over the Republican base, months after a spring retribution tour where he drove a series of G.O.P. opponents out of Congress. And Ms. Graham’s win came as another Trump-endorsed candidate, Mike Mazzei, prevailed in a hotly contested Republican primary runoff for governor of Oklahoma.

Some of the luster had seemed to come off Mr. Trump’s political brand in recent weeks. His approval ratings have drooped, his party’s midterm outlook has darkened and his chosen picks in several races for governor and the House have fallen short.

While Ms. Graham emerged triumphant in South Carolina on Tuesday, it came at a cost. As Mr. Trump and his party struggle to defend Republican congressional majorities, he expended time and energy in a race for a solidly red seat expected to have no bearing on control of Congress.

Still, in South Carolina, Republican voters signaled that the party’s political identity, and perhaps its fortunes, remain tightly intertwined with Mr. Trump even as the party begins to imagine what it might look like after his presidency.

“They still trust the president,” said Ida Martin, a Republican state executive committeewoman from Williamsburg County. “Trump came for her, and people showed up.”

Ms. Graham’s triumph may have reflected the loyalty that plenty of Republican voters in South Carolina felt for her brother, who represented the state in the Senate for more than two decades. But it underscored the president’s ongoing ability to bend primaries to his will. Some South Carolina voters said that they had been on the fence — and that the president’s intervention had been decisive in their vote.

“South Carolina is truly Trump country,” Ms. Graham said at her election night party, thanking the president for his support.

Mr. Trump’s grip on his party has sometimes seemed most solid in the South.

It was there that he scored some of his most impressive victories of primary season: Voters followed his instructions by ousting Senator Bill C***idy of Louisiana and Representative Thomas M***ie of Kentucky. And they sided with his choice for Senate in Georgia, elevating Representative Mike Collins despite Republican warnings that the congressman’s right-wing politics might hurt the party’s chances in a contest that could determine control of the Senate.

The voters who came through for Mr. Trump in South Carolina did not have to worry much about general-election implications; the winner of the primary is widely expected to prevail in November. But they did have to look past — or at least accept — the unique particulars of Ms. Graham, who was hardly known before the summer, and who did not appear to have many firmly held policy positions beyond a conviction that transgender girls should not play girls’ sports.

“I don’t speak politician,” Ms. Graham told Fox News as she ran for a distinctly powerful political office. Of her flub on the debate stage after being asked about the importance of Taiwan to U.S. interests, she said: “Of course, Taiwan is our friend. But I think people in South Carolina are more worried about making ends meet. They’re concerned about boys in girls’ sports.”

Ms. Graham had never held elected office before her brother’s death. She ***umed his seat through the appointment of the state’s Republican governor, Henry McMaster.

Her lack of experience became a dominant theme of her runoff against an experienced politician: Representative Ralph Norman, a five-term lawmaker backed by sitting senators and Nikki Haley, the state’s former Republican governor. And cracks in Mr. Trump’s typically Teflon endorsement record had emerged just a week earlier, when he failed to lift Republican primary candidates to victory in Florida and Wyoming. Earlier this year, Republican voters in South Carolina had defied the president’s wishes in the state’s race for governor.

Mr. Trump went to extraordinary lengths to avoid another loss in South Carolina, stepping up his efforts in the final days of a race he essentially stage-managed from the start.

By the day of the runoff, he had visited the state for a rally and joined a virtual rally on election eve. His super PAC made a rare injection of money into the race to help Ms. Graham, flooding voters with calls and texts imploring them to get behind her.

“Your state is so important to me,” Mr. Trump said at the virtual rally before emphasizing how personal the race was to him. “I love her. I think she’s great. I asked her to do it — I got her into this whole thing. I have to make sure she gets in.” (It was not clear if Mr. Trump had, in fact, asked her to run.)

The president also pressured a former contender in the race, Representative Russell Fry, to support Ms. Graham. Mr. Fry followed through, issuing an endorsement declaring that Mr. Trump needed “fighters and allies in the Senate.”

The president was asking fatigued South Carolina voters — who had already cast ballots in three elections since early June — to come back for one more primary. But the impact of his appeals was clear: Hundreds of thousands of voters flocked to polls across the state, defying a trend in which runoff turnout is typically far softer than in initial primaries.

Bob Heckman, a longtime consultant to Lindsey Graham who worked on Ms. Graham’s campaign, said the president’s team had “pushed all their chips into the table” to support her candidacy.

“It helped set the narrative for the campaign that Darline was the Trump candidate,” he said from Ms. Graham’s watch party, as Elton John’s “Rocket Man” played and supporters waited to greet their new nominee.

Tiffany Tan contributed reporting.