Ames, Iowa - Presidential candidate Nikki Haley responded after her challenger Donald Trump claimed she is "not tough enough" for the presidency as the two prepare for the Iowa caucuses.

On Sunday, Haley did an interview with CNN host Dana Bash where she was asked about Trump's most recent criticism.

"Everybody that's ever worked for me or worked with me, no one ever questions my toughness," Haley explained.

"He's saying this because now he knows he's in trouble. Now he knows this is becoming a two-person race. So I know that he knows the truth. It doesn’t bother me at all."

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During a rally earlier that day, Trump told a crowd of his supporters that he believed Haley – who he appointed as ambassador to the United Nations during his presidency – was "not right to be president," arguing that she has "the wrong thought process, the wrong policy," and is "not tough enough" to deal with foreign leaders.

In her interview, Haley also shared that she found Trump's criticism "comical" because "he always used to tell people, 'don't mess with her. She's tough.'"

Throughout the GOP primaries, Trump has maintained a significant lead with Republican voters despite facing 91 criminal charges and other legal issues.

Haley has recently seen notable bumps in the polls and high-profile endorsements, but not nearly enough to beat the former president in Iowa and most states across the US.

In a final poll conducted ahead of the caucuses, Trump received 48% support in Iowa while Haley only received 20%.

While Trump is expected to win the state, Haley may fare better in New Hampshire next week where Trump is leading her by only one point.