The honeymoon period of Nikki Haley's presidential campaign is over.

After enjoying weeks as a rising star, the former South Carolina governor is facing a heightened level of scrutiny not just from her GOP rivals, but from voters.

That new dynamic was on display during a swing through New Hampshire where Haley stumbled over a question on the cause of the Civil War by failing to mention slavery and was accused of being a flip flopper by a nine-year-old child over her unwillingness to criticize former U.S. president Donald Trump.

Haley has shown an ability to appeal to independents and moderates by eschewing culture war fights, calling for consensus on issues such as abortion and attempting to avoid controversy. While those qualities have made her an appealing general election candidate, they have led to unforced errors, embarrassing clarifications and tense exchanges with voters ahead of the official start of the primary next month.

It has also undercut one of the central arguments of her campaign, that she's someone who is willing to give voice to things others are afraid to say.

"There's no flip flopping," she told reporters during a gaggle Thursday after she clarified that "of course" she believed the Civil War was about slavery. "I've never been a flip flopper. What I do is I speak hard truths, whether people like it or not, and I let the chips fall where they may."

During one exchange in Lebanon, N.H., a voter said she was "coming up short" on "moral clarity" compared to former New Jersey governor Chris Christie.

"This is a chance to redeem yourself after last night's slavery thing," the voter said. "Would you be able to say categorically that you won't accept being Trump's vice-president? The reason, I got this ballot here and I'm trying to figure out if I'm going to mark you or Chris Christie."

Haley stopped short of saying she would never accept the vice-presidential slot from Trump, but repeated her stance that she "doesn't play for second."

The difficult voter questions Haley has faced this week appear to be drawn from either her own history or criticisms from opponents. She's also facing more questions about whether she would pardon Trump or be his vice-president, spurred by comments from Christie, DeSantis and others.

"When you try to be everything to everyone, you're nothing to anyone," biotech entrepreneur Vivek Ramaswamy, who has faced his own criticisms for shifting policy stances, wrote in a social media post Thursday. "A perfect puppet for the corrupt establishment."

Florida Gov. Ron DeSantis described Haley's initial remarks on the root causes of the Civil War as an "incomprehensible word salad" and said it showed his opponent isn't "ready for primetime."

"The minute that she faces any kind of scrutiny, she tends to cave," he told reporters Thursday.

Democrats have also seized on Haley's comments. President Joe Biden wrote in a succinct that the Civil War was about slavery. Democratic National Committee chair Jaime Harrison, the former chair of the South Carolina Democratic party, said he was "disgusted" but the comments, adding that "this is what Black South Carolinians have come to expect from Nikki Haley, and now the rest of the country is getting to see her for who she is."

The Haley campaign has attributed the extra scrutiny – from Republicans and allies of Joe Biden – as a natural result of rising in the polls.

"Everyone from Joe Biden to Donald Trump is attacking Nikki for one reason: she's the only candidate with momentum," Haley campaign spokesperson Olivia Perez-Cubas said in a statement. "For months, Nikki has been talking to every voter and taking every question, and she'll continue to do that."

A found that 44 per cent of likely New Hampshire primary voters support Trump, followed by 29 per cent who back Haley, 11 per cent who back DeSantis and 10 per cent who would vote for former Christie. Last week, MAGA Inc., the super PAC supporting Trump, rolled out its first ad against Haley, focused on her stance on her state's gas tax as governor.

A Wall Street Journal found Haley running ahead of Biden by 17 points, 51 per cent to 34 per cent, while Trump narrowly edged Biden by just four points.

It's not clear how Republican primary voters will react, if at all. Teresa Frey, a voter who saw Haley in Plymouth, N.H., Thursday said she thought the Civil War question was "random."

"I heard that and I thought why was that question even asked," she said. "Was it somebody trying to get her off her game? I know she … I feel like she wasn't obviously prepared for that."

Christie, who has faced calls to drop out to consolidate the non-Trump vote, dedicated several minutes of his Epping, N.H., town hall Thursday to Haley's stumbles.

Christie said Haley is "unwilling to offend anyone by telling the truth," pointing to her responses to questions of whether Trump is fit to be president.

Christie argued if Haley is unwilling to say slavery caused the Civil War "because she's afraid of offending constituents in some other parts of the country" and unwilling to say Trump is unfit for office because she "harbours in the back of her mind being vice-president or being secretary of state," then she will not be able to stand up to foreign adversaries, members of the other party or "forces in our own party, who want to drag this country deeper and deeper into anger and division and exhaustion."

The Civil War debacle is the latest example of her rivals pouncing on one of her stumbles. DeSantis and others piled on Haley last month after she called for ID verification on social media platforms, which would have eliminated anonymous accounts. Haley soon walked the policy back.

On abortion, Haley has said throughout the campaign that Republicans must reach a "consensus" policy, and warned that her party must be honest with voters about how difficult it would be to get 60 Senate votes to pass a federal ban. But during an event in Iowa last month she said she would have signed a six-week abortion ban in South Carolina if she were still governor. Christie accused her of saying one thing in Iowa and another to Granite State voters.

The question on the Civil War, to which Haley initially responded by saying the war was about "freedoms and what people could and couldn't do" highlighted her record defending the Confederate flag and states' right to secede from the U.S. while campaigning for governor in 2010. In the past she has called the Civil War a battle between "change" and "tradition."

On race specifically, Haley has tried to find the middle ground between acknowledging racism in her state – and, as her profile grew, the country — and painting America as having moved past its dark history. On the campaign trail she emphasizes that America "isn't racist" but is "blessed."

Haley, who served as South Carolina governor from 2011 to 2017, is well known for her role in calling for the Confederate flag to be removed from the statehouse grounds in the days after a white supremacist killed nine worshippers at a church in Charleston in 2015. But that decision came after she defended the flag during her 2014 gubernatorial bid.

She referenced that moment as she cleaned up her answer on the cause of the Civil War.

"I say that as a southerner, I say that as a southern governor who removed the Confederate flag off the statehouse grounds and I say that as a proud American of how far we have come," Haley said Thursday.