Former President Trump, while speaking Sunday at a rally in Indianola, Iowa, on the day before the Iowa caucuses, said one of his Republican presidential nomination opponents, Nikki Haley, is not ready for the job.

Trump told the crowd there is a lack of loyalty in politics, adding that, to a lesser extent, there has been a lack of loyalty from Haley.

He explained that he gave Haley her position of U.N. ambassador when she was governor of South Carolina because he wanted then-Lt. Gov. Henry McMaster to be governor of the state.

"Nikki did a good job. She was out there, but she’s not ready to be president," Trump said. "I know very well … and honestly, she’s not tough enough."

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Nikki Haley and Donald Trump recent images cropped side by side

Nikki Haley has been floated as a potential vice presidential running mate for former President Trump. (Getty Images)

The comments came hours after the former South Carolina governor issued a challenge to Trump during an interview with Fox News Digital ahead of Monday's Iowa caucuses.

"It’s you and me now," she said after the release of polls that showed her in second place against Trump and ahead of fellow GOP presidential candidate Florida Gov. Ron DeSantis.

Trump maintains a commanding lead over the field, according to polling.

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Former President Donald Trump picks up the pace on his visits to the first caucus state of Iowa

Former President Trump says one of his Republican opponents for president, Nikki Haley, is not ready for the job. (AP Photo/Charlie Neibergall/File)

On Sunday morning, Fox News asked Trump if he thinks he'll receive more than 50% of the vote in the caucuses.

"I don’t know, I think we are doing very well," Trump said.

The former president is the commanding front-runner in the latest polls in Iowa as well as in national surveys in the GOP presidential nomination race as he makes his third straight White House bid.

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Nikki Haley in Iowa

Nikki Haley, former ambassador to the United Nations and a 2024 Republican presidential candidate, speaks during a campaign event in Iowa City on Jan. 13, 2024. (Alex Scott/Bloomberg via Getty Images)

He grabbed 50% support, or higher, in a slew of polls over the past month in Iowa. And he stood at 48% support in the final Des Moines Register/Mediacom/NBC News poll of likely Republican caucus goers that was released Saturday night.

His closest rivals – Haley and DeSantis – stood at 20% and 16%, respectively, in the new survey.

HALEY KNOCKS MEDIA EXPECTATIONS BUT LOOKS TO ‘BIG SHOWING’ IN IOWA

The survey conducted by pollster Ann Selzer, which is closely watched and highly anticipated, has a well-earned tradition of accuracy in past GOP presidential caucuses and is considered by many as the gold standard for Iowa polling.

Paul Steinhauser and Andrew Murray of Fox News Digital contributed to this report.