One day after Donald Trump endorsed a primary challenger against Republican Rep. Nancy Mace, the first-term lawmaker from South Carolina showcased that she was one of the former president's earliest supporters.

And in a video posted to social media on Thursday, Mace warned that if Katie Arrington, her Trump-backed challenger, wins the GOP primary, the Democrats would likely recapture South Carolina's coastal-based 1st Congressional District.

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"I remember in 2015 when President Trump announced his run, I was one of his earliest supporters. I actually worked for the campaign in 2016. I worked at seven different states across the country to help get him elected," Mace highlighted in her video, which was recorded as she stood in front of Trump Tower in New York City.

"I supported him again in 2020 because of policies I believed in," Mace noted. "He brought American jobs back. He lowered our taxes…he made America safer and took on China directly.

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Trump, as he endorsed Arrington on Wednesday, called Mace a "an absolutely terrible candidate" who he claimed was "not at all representative of the Republican Party to which she has been very disloyal."

Mace, in her video, noted that "I won this seat back for Republicans in 2020," and taking aim at Arrington, she argued, "If you want to lose this seat once again in the midterm election cycle to Democrats, then my opponent is more than qualified to do just that."

The district was represented for much of the last decade by former Republican Gov. Mark Sanford. But Arrington, with Trump's support, challenged and defeated Sanford in the 2018 GOP primary. But she lost the general election by a razor-thin margin to Democrat Joe Cunningham.

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Two years later, in 2020, Mace narrowly edged Cunningham as the GOP flipped the seat back from blue to red.

Mace was not one of the 10 House Republicans to vote 13 months ago to impeach the then-president on charges he incited the Jan. 6, 2021, attack on the U.S. Capitol by Trump supporters aiming to disrupt congressional certification of now President Biden's Electoral College victory in the 2020 election.

But she did publicly say that Trump's rhetoric leading up to the storming of the Capitol "put all of our lives at risk."

Nancy Mace

Rep Nancy Mace speaks with reporters at the U.S. Capitol on Oct. 21, 2021. (Anna Moneymaker/Getty Images)

And in October, Mace was the lone South Carolina Republican to join congressional Democrats in voting to hold former Trump White House senior aide Steve Bannon in contempt of Congress for defying a subpoena issued by the House select committee investigating the riot at the Capitol. 

Soon after Mace posted her video, Arrington fired back, asking why the congresswoman was in New York City if her constituents were in South Carolina.

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Arrington hit back at Mace over the video, asking why she was in New York City if her constituents were in South Carolina. 

In a tweet, Arrington asked "are you in NYC to fundraise with the progressives? What does NYC have to do with the Lowcountry?"

The former president's backing of Arrington came two days after former South Carolina Gov. Nikki Haley, who served as ambassador to the United Nations during the Trump administration, endorsed Mace.

South Carolina's primary is scheduled for June 14.