Nikki Haley on Friday called Donald J. Trump “totally unhinged” after a failed attempt by one of his allies to push the Republican National Committee to declare him the party’s presumptive nominee, escalating her attacks on his mental acuity.
Ms. Haley, the former South Carolina governor and Mr. Trump’s ambassador to the United Nations, cast her onetime boss as increasingly antagonistic during an appearance on Fox News.
“Let’s look at the last 48 hours,” Ms. Haley said, and she went on to assail him over his combative rhetoric in his victory speech Tuesday in New Hampshire.
“He throws an absolute temper tantrum, talking about revenge,” she said. “Then he goes and says that he’s going ban anyone from MAGA that donates to me.”
“I mean he’s totally unhinged,” she said.
She also accused him of being behind an R.N.C. member’s plan to use a resolution to try to force the party to say the nominating contest was effectively over. But the plan was withdrawn after Mr. Trump rejected it in a post on his Truth Social website.
Ms. Haley, who lost to Mr. Trump, the G.O.P. front-runner, by about 11 percentage points on Tuesday in the New Hampshire primary, has vowed that she will continue her uphill campaign.
Mr. Trump’s campaign spokesman, Steven Cheung, used Mr. Trump’s derogatory nickname for Ms. Haley, “birdbrain” and said she “is trying to grasp at straws to gaslight voters because she’s nothing more than a Democrat with America Last policies that will destroy the country.”
The tenor between Ms. Haley and Mr. Trump has grown increasingly caustic since the race narrowed to just the two of them. Ms. Haley first hit at his age in the days ahead of the New Hampshire primary, suggesting that “there is a decline.” Mr. Trump seethed at her refusal to quit the race in his victory speech.
In the Fox interview, she pushed back against the narrative that her loss in New Hampshire — where it was a two-candidate race — and her third-place finish in the Iowa caucuses on Jan. 15 had left her an extremely narrow pathway to the nomination. Mr. Trump holds a commanding polling lead in South Carolina, her home state and the next major contest between them.
Ms. Haley also said that she had spoken to Ronna McDaniel, the Republican National Committee chairwoman, who told Fox News on Tuesday after Mr. Trump’s victory: “We need to unite around our eventual nominee, which is going to be Donald Trump.”
“I let her know how disappointed I was,” Ms. Haley said.
Mr. Trump has ratcheted up the pressure on Ms. Haley to leave the race, suggesting that it is futile for her to move forward to the next contests. And he has argued that a protracted primary battle would squander time and money from the broader objective of challenging President Biden in the November election.
“She is going to be embarrassed and she will never be able to run for public office again,” Mr. Cheung said on Friday.
Ms. Haley, for her part, has long argued that she is better positioned to beat Mr. Biden than her former boss is.
Alyce McFadden and Jazmine Ulloa contributed reporting.
