Nikki Haley has been endorsed by a powerful conservative group founded by the Republican mega-donor Charles Koch, in a move that could dramatically shake up the 2024 Republican primary.
Americans for Prosperity Action (AFP), a political action committee founded by Mr Koch and backed by other wealthy conservatives, said it was “proud to throw our full support” behind Ms Haley.
Emily Seidel, senior adviser for the group, said the 51-year-old former US ambassador to the UN “will have the full weight and scope” of the group’s “unmatched grassroots army and resources” in her presidential bid.
The intervention is a major boost to Ms Haley roughly seven weeks before the contest begins in Iowa, a critical proving ground for Donald Trump’s challengers.
Mr Trump holds a commanding, double-digit lead over the field but Ms Haley has gained momentum after a string of fiery TV debate performances and is presenting herself as the most credible alternative to the former president.
AFP’s backing is a blow for Ron DeSantis, the 45-year-old Florida governor whose bid to take on Mr Trump has been in free fall since the summer.
Andrew Romeo, a spokesman for Mr DeSantis, said the endorsement represented an “in-kind” donation to the Trump campaign, arguing that Ms Haley has no path to victory.
“Like clockwork, the pro-open borders, pro-jail break bill establishment is lining up behind a moderate who has no mathematical pathway of defeating the former president,” Mr Romeo said.
“No one has a stronger record of beating the establishment than Ron DeSantis, and this time will be no different.”
Ms Haley has challenged Mr DeSantis’ second-place position with a bump in donations and support in recent weeks and is increasingly being seen as Mr Trump’s strongest rival.
She has benefited too from the early exit of Mike Pence, the former vice-president, and Tim Scott, the South Carolina senator, whose supporters and donors have regrouped behind Ms Haley.
Charles Koch, like his late brother David until his death in 2019, has been a power player in Republican politics for decades.
The billionaire brothers were executives of the family business Koch Industries, one of the largest privately held companies in the US.
Charles Koch was an early backer of the populist grassroots Tea Party movement that materialised in response to Barack Obama’s emergence on the national political scene, but later said he regretted his support.
The Koch-backed AFP declined to endorse Mr Trump in the 2016 and 2020 presidential campaigns but has a formidable warchest.
It spent around $69 million on Republican races in the 2022 midterm elections. In its last public disclosure in June, AFP said it had raised more than $70 million, with $25 million coming directly from Mr Koch.
While the group has not said how much it will spend on Ms Haley, it has promised to deploy “the largest grassroots operation in the country and a presence in all fifty states”.
AFP vowed to work to block Mr Trump earlier this year amid concerns over his electability and, after weighing his rivals for months, said it was endorsing Ms Haley because she “has what it takes to lead”.
However, they face severe headwinds, with Mr Trump leading the Republican field with around 60 per cent of support from the party’s voters in national polling.
Mr DeSantis and Ms Haley have around 12 per cent and 10 per cent respectively according to polling aggregator FiveThirtyEight.
However, the picture is slightly more mixed in the early voting states, where many voters have yet to make up their minds and Mr Trump’s lead could be challenged.
Both Mr DeSantis and Ms Haley hope to provide an upset to Mr Trump’s frontrunner status in Iowa.
AFP already has spent millions of dollars on advertising in the early states. One flyer in Iowa has images of Mr Trump and Joe Biden and reads: “You can stop Biden…by letting go of Trump.”