Wearing “Trump is too chicken to debate” stickers, Mike and Susan Strouse, Republicans who count themselves as die-hard Haley supporters, said they had been following her rise since those days. They had voted for Mr. Trump twice but did not believe him to be a viable choice for president after his supporters stormed the U.S. Capitol on Jan. 6, 2021.

“I just feel in my heart that she is the best,” Mr. Strouse said.

Introducing Ms. Haley earlier, Mayor Foster Senn of Newberry recalled that in 2010, just like now, Ms. Haley took on the establishment, challenging rivals no one thought she could beat. The state’s current establishment, including the governor and its two U.S. senators, has backed Mr. Trump over her. But while the opera house has a capacity of more than 1,000, Ms. Haley spoke outside, to an audience of about 150. On Monday, at a Harley-Davidson dealership in Elgin, S.C., she addressed around 50 people, and some chairs that had been set up went unfilled.

Her other visits included Bamberg, her rural hometown near Columbia, which drew people who said they knew and liked Ms. Haley and her family growing up. The town’s mayor, who recalled stories of Ms. Haley from childhood, would not commit to voting for her.

All the while, her regular boasts about South Carolina’s economy under her leadership, her personal story and her calls to imagine a different country “where there wasn’t so much anger and division” took a back seat to her fervent attacks on Mr. Trump.

In the last few weeks, she has reframed her stump speech to attack the former president over his mental acuity, legal issues and his role in the collapse of a Republican-led deal in Congress to address the arrival of migrants at the southern border. She has sought to brand Mr. Trump and President Biden as “grumpy old men.” She has chastised fellow members of her party for feeding into Mr. Trump’s “chaos.”