Nikki Haley, the former South Carolina governor and Republican presidential hopeful, on Thursday walked back her stumbling answer about the cause of the Civil War, telling a New Hampshire interviewer, “Of course the Civil War was about slavery.”

Her retreat came about 12 hours after a town-hall meeting in New Hampshire, a state that is central to her presidential hopes, where she was asked what caused the Civil War. She stumbled through an answer about government overreach and “the freedoms of what people could and couldn’t do,” after jokingly telling the questioner he had posed a tough one. He then noted she never uttered the word “slavery.”

“What do you want me to say about slavery?” Ms. Haley replied. “Next question.”

Speaking on the radio show The Pulse of New Hampshire on Thursday morning, Ms. Haley, who famously removed the Confederate battle flag from the grounds of the South Carolina Capitol in Columbia, said: “Yes I know it was about slavery. I am from the South.”

But she also insinuated that the question had come not from a Republican voter but from a political detractor, accusing President Biden and Democrats of “sending plants” to her town-hall events.

“Why are they hitting me? See this for what it is,” she said, adding, “They want to run against Trump.”

In recent polls, Ms. Haley has surged into second place in New Hampshire, edging closer to striking distance of former President Donald J. Trump. To win the Granite State contest on Jan. 23, the first primary election of 2024, she will most likely need independent voters — and possibly Democrats who registered as independents. That is how Senator John McCain of Arizona upset George W. Bush in the state’s 2000 primary.