Former Trump rival Nikki Haley defended her decision to throw her support behind the GOP nominee after Liz Cheney called her principles into question.

Cheney, a one-time rising Republican Party star who became a top GOP critic of former President Trump, endorsed Vice President Kamala Harris last week. She then called out Haley on ABC Sunday for saying she's "on standby" to campaign for the GOP nominee.

"I respect [Cheney's] decision, but she can't say my decision is not principled," Haley told "Fox & Friends" in response, Monday. "It actually is."

"We can either vote based on style or we can vote on substance. I'm voting based on substance. I'm looking at the fact we can't live the next four years like we did the last four years. This is no contest. Harris raised taxes. Trump reduced taxes. Harris wants to stop any energy production. Trump built it up. Harris is weak on national security. Trump was strong on national security. Harris has allowed the border to be infiltrated by 8 million people. Trump was much harder on the border."

HARRIS STOPS IN KEY SWING STATE THAT TRUMP CHARGES VP AND BIDEN ‘DISRESPECTED’

Cheney told "This Week" yesterday that she can't understand the former South Carolina governor's position "in any kind of a principled way" following a contentious GOP primary.

"The things that she [Haley] said that she made clear, when she was running in the primary, those things are true," Cheney said. "Casting a vote for Donald Trump or writing someone in means that you've made the decision in too many instances that so many elected Republicans have made, which is, is to abandon the Constitution."

In response, Haley said she's "happy to be helpful" to Trump's campaign in order to stop a Harris administration.

"This is about my family. This is about America. These are about issues. We should be very clear. If you don't like him, say you don't like him, but you can't say that his policies are worse than Kamala Harris'. That's just not a fact."

Haley added that Trump needs to work on getting support from "conservative and moderate Republicans, suburban women, independents, conservative Democrats," and predicted that this will be a "tight election." 

She urged Trump and running mate JD Vance to "focus on the policies" to win over voters.

Liz Cheney

Former Republican Congresswoman Liz Cheney joined the hosts of "The View" on Wednesday and was asked twice if she would vote for President Biden over Donald Trump. (Screenshot/ABC/TheView)

Minutes after Cheney's Harris endorsement, the Trump campaign posted on social media an interview of Cheney on Fox News four years ago taking aim at the current VP.

"Her voting record in the Senate is to the left of Bernie Sanders and Elizabeth Warren," Cheney argued at the time. "It's very clear, she is a radical liberal."

Cheney was ousted from Congress in 2022 after losing her Wyoming district's primary to a candidate backed by Trump.

Cheney — who has argued that the former president is a "liar," a "con man" and a potential "tyrant" who, if elected again, would "torch the Constitution" — vowed after leaving Congress that "I will do everything I can to make sure [Trump] is never anywhere near the Oval Office again."

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Fox News' Paul Steinhauser contributed to this report.