Nikki Haley is sharpening contrasts with Donald Trump in the South Carolina primary's closing days

COLUMBIA, S.C. -- Nikki Haley is using the closing days of her South Carolina Republican primary matchup with Donald Trump to hone her argument that she is the lone remaining candidate who can unite Americans, despite the former president's electoral wins thus far and his popularity in her home state.

It's a tall order for Haley as South Carolina prepares to vote on Saturday. Trump's 2016 primary win helped cement his front-runner status, and he boasts support from all of the state's top elected leaders and all but one of its congressional Republicans.

But Haley has maintained that her ability to stick it out in the race, having outlasted a dozen also-ran candidates, means that she's in it for the long haul. Her amped-up fundraising could keep her going despite her earlier losses to Trump.

Part of Haley's argument is her continued showcase of her foreign policy knowhow, having served as Trump's United Nations ambassador for two years, as more and more of her campaign appearances feature areas in which she says she would have acted differently than her former boss.

"I will absolutely put the hammer on our NATO countries that they do have to carry their weight, but you do that behind closed doors," Haley said Sunday during a town hall on Fox News with John Roberts, broadcast from a venue in downtown Columbia, South Carolina.

It was a reference to Trump's warning to NATO allies during a campaign rally earlier this month that he "would encourage" Russia "to do whatever the hell they want" to countries that are "delinquent" -- nations that in his view are not doing their part in that alliance. NATO's leader said Trump's attacks on long-standing international alliances and foreign aid could undermine security and put American and European forces at risk.

"We should make sure we tell our partners it's in their best interest to hold their own weight," Haley said Sunday. She said "Trump did it by saying he was going to encourage Putin to invade our allies. That's the wrong way."

She sharpened those comments during a Monday morning campaign stop in the central South Carolina city of Sumter, home to an Air Force base as well as many military veterans. She said Trump is "siding with a thug" in Vladimir Putin, whom she called "a dictator who killed his political opponents."

It's an argument she makes in a new television ad, part of a $6 million advertising flurry Haley has released in the final weeks of the campaign across her state.

In "Unite," which begins airing Monday and was shared before its launch with The Associated Press, Haley argues she is the only choice among the remaining candidates who can handle disputes with foreign leaders in a way that will keep America on solid footing abroad.

"When your enemies think you're weak, your leader must be strong," a narrator says, over images of foreign leaders including Chinese President Xi Jinping and Putin. "When your country is divided, your president must unite us."

The ad argues that Haley "provided moral clarity during our darkest hours," over headlines from coverage of the racist slaying of nine Black parishioners at a Charleston church in 2015, during Haley's second term as South Carolina governor. "What's next? That's up to you."

Saying Sunday -- as she has throughout her campaign -- that she's "OK being the underdog now," Haley has been firm in saying that she has never lost a race and believes voters will see her as the right choice to shift away from the "chaos" she says follows Trump. She also frequently notes that, while Trump has won the earliest contests, she has been ascendant, pointing to the shrinking margins between her totals and Trump's in the Iowa and New Hampshire contests.

But over the weekend, Haley also began making an appeal to South Carolinians who typically vote in Democratic primaries, for Saturday's vote, a message she also echoed during campaign events on Monday.

She noted that anyone who didn't vote in the Feb. 3 Democratic primary -- which attracted under 5% of eligible voters statewide -- can vote in this one, as she bid for crossover support from people who want to cast a vote against Trump.

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Meg Kinnard can be reached at http://twitter.com/MegKinnardAP