The political network created by the billionaire industrialist Koch brothers announced Sunday that it was suspending its support for Nikki Haley in the presidential primaries following her latest defeat in South Carolina.

The group, Americans for Prosperity Action, had spent tens of millions of dollars trying to elevate Ms. Haley and prevent the renomination of Donald J. Trump, but had already dramatically slowed its spending in the Republican race after Ms. Haley fell short in the election. the New Hampshire primary last month. The organization made its decision official on Sunday.

“Given the challenges in the primary states ahead, we do not believe an outside group can make a material difference to broaden her path to victory,” Emily Seidel, the CEO of Americans for Prosperity Action, wrote in an email email to staff. . The email was first reported by Politico.

Ms. Seidel wrote that the group would now focus on House and Senate races, adding that the conservative organization remained concerned about the political aftershocks of Mr. Trump winning the Republican nomination.

“If Donald Trump is at the top of the Republican ticket, the risk of one-party rule by a Democratic Party captured by the progressive left is high,” she wrote.

Ms. Seidel described how the last three elections had shown “what we can expect from voters who have consistently rejected Donald Trump and his impact on the Republican party brand.”

Ms. Haley’s campaign had announced that it had raised $1 million in the less than 24 hours since polls closed in South Carolina on Saturday and she lost her home state. She has pledged to stay in the race through Super Tuesday, March 5.

In a statement, the Haley campaign praised the Americans for Prosperity Action as an ally.

“We thank them for their tremendous help in this race,” the statement said. “Our fight continues, and with over $1 million coming in from grassroots conservatives in the last 24 hours, we have plenty of fuel to keep going. We have a country to save.”

The group’s endorsement, announced in November, was crucial for Ms. Haley. It came as she tried to gain traction with Mr. Trump, especially given how small her team was at the time. It gave her access to a direct-mail operation, field workers to knock on doors and people to make calls to potential voters in Iowa and other states.

Despite these efforts, however, Ms. Haley came a distant second to Mr. Trump in Iowa. One person close to the network said that in its latest stretch into South Carolina, it had focused on reaching grassroots voters, rather than advertising.

After word of the group’s withdrawal became public, Trump posted on his social media website that Charles Koch “and his group were played as suckers from the start!”

Sen. John Fetterman of Pennsylvania is backing Rep. Andy Kim of New Jersey in the primary to unseat Sen. Bob Menendez, the embattled Democrat charged in a federal corruption case. fire a colleague.

Mr. Fetterman, Mr. Menendez's fiercest Democratic critic in Congress who has repeatedly called for him to resign, is the first sitting senator to endorse a candidate in the race. In an interview, he explained his decision to intervene in a primary and take out a fellow incumbent senator, bluntly stating that “anything would be an upgrade over Menendez.”

Mr. Kim, a three-term congressman who represents a southern New Jersey district that former President Donald J. Trump won twice, is running for the seat against Tammy Murphy, New Jersey's first lady and a primary candidate who former is president. registered Republican. Ms. Murphy has locked up much of the institutional support in a state where county leaders have enormous power in primaries but struggle to gain traction with the base.

Mr. Kim leads by double digits in some recent polls.

In an interview, Mr. Fetterman said he was “excited” about Mr. Kim and that Ms. Murphy’s political background — she only changed her party affiliation from Republican to Democratic in 2014 — gave him pause.

“One of the most important things is that we have a reliable Democratic voice,” Fetterman said. 'We have to run this table in '24 to keep the majority. But we must count on every Democratic vote. Andy Kim is the kind of man we can count on.”

Mr. Fetterman said Ms. Murphy was probably “a nice woman, but the last time I had to deal with a Republican from New Jersey, it was my own race.” Mr. Fetterman defeated Dr. in 2022. Mehmet Oz, the Republican candidate for Senate, whom he mercilessly targeted as a famous carpetbagger from the Garden State.

“I wouldn't want to risk having someone who might be hesitant when we have to cast a solid Democratic vote in a very, very divided Senate like us,” Mr. Fetterman said. Mr. Kim, he said, is a well-known figure and a “leading member of Congress who has worked very, very hard.”

Mr. Kim said he appreciated the support in a Senate race that he said would be the most dramatic in New Jersey history.

“To have someone who is a sitting senator, who knows the job, knows the role of a legislator right now, and also just understands the crazy, chaotic moment that we're living in right now, that's something that stands out,” Mr. . Kim said in an interview. “Senator Menendez is still here and working. That has complicated this dynamic. I appreciate Senator Fetterman's willingness to lean forward. That's not necessary. It is a very complicated race.”

Mr. Kim, a soft-spoken former national security official in the Obama administration, cast himself as the proven candidate New Jersey voters need to restore their faith in politics.

“Right now, 84 percent of people in New Jersey believe their politicians are corrupt,” he said, calling the indictment against Mr. Menendez the “breaking point” for many voters. “At a certain point you think: how can democracy function at such a level of lack of trust? Many people want someone who can be there from day one and get the job done right away.”

Mr. Kim echoed Mr. Fetterman's charge that Ms. Murphy would not necessarily be a reliable Democratic voice in the Senate, noting that she switched parties long after the Affordable Care Act was enacted.

“She voted in every Republican primary during the Obama administration,” Kim said. “She'll have to explain that.”

The race is complicated in part because the seat isn't technically open. Mr. Menendez, who resigned as chairman of the Foreign Affairs Committee after being accused in September of accepting bribes and gold bars in exchange for political favors, has denied any wrongdoing and accused the Justice Department of framing him in a public smear campaign attacked.

He has defiantly refused to resign, although he has not formally announced a re-election campaign. Polls show him with 6 percent favorability among New Jersey voters. Mr Fetterman said: “I don't really trust the polls. Six percent actually seems like a lot for his approval.”

Mr. Kim was also scheduled to announce endorsements Thursday from six Democratic House members from Pennsylvania: Reps. Dwight Evans, Madeleine Dean, Chrissy Houlahan, Mary Gay Scanlon, Susan Wild and Brendan Boyle.