Her remarks in Iowa on Friday were not a drastic departure from her previous stance, but her gesture of support for a ban at six weeks after conception, when many women don’t yet know they are pregnant, could pose a political risk.

Ms. Haley is performing well in New Hampshire, the second state to vote in the Republican primary, where voters tend to be more supportive of abortion rights. (The state currently bans abortions after 24 weeks.) And wealthy G.O.P. donors, who have paid more attention to Ms. Haley after her strong debate performances, are also more moderate on abortion.

Democrats were quick to pounce on the comments, a sign that they see Ms. Haley, who is polling well against President Biden, as a threat. Even as Ms. Haley was still addressing the crowd at a hotel ballroom in Des Moines, where was joined onstage by Mr. DeSantis and the entrepreneur Vivek Ramaswamy, the Biden campaign posted a video of Ms. Haley on X, the social media network formerly known as Twitter. The video contained only one word of her answer.

“Q: Would you sign a 6-week abortion ban if you were governor?” the post said. “Haley: Yes”

In a statement, Ammar Moussa, a Biden campaign spokesman, said, “Nikki Haley is no moderate — she’s an anti-abortion MAGA extremist who wants to rip away women’s freedoms just like she did when she was South Carolina governor.”

While serving as governor in 2016, Ms. Haley signed a ban on the procedure at 20 weeks in the state.

At the most recent Republican debate, in Miami this month, Ms. Haley said that as president, she would sign an abortion ban of any length passed by Congress. But she also echoed her belief that Republicans would not find enough votes to do so. Instead, she said Americans should “find consensus” where possible on issues such as banning abortions later in pregnancy, promoting adoption and access to contraception and not criminally charging patients who get abortions.