Republican Nikki Haley, who until this week had run a disciplined and largely error-free presidential campaign, has been forced into an uncomfortable and unexpected new chore: doing cleanup on a blunder related to the Civil War and slavery.

The former South Carolina governor and United Nations ambassador was forced into defensive mode after she omitted slavery from an answer she gave at a New Hampshire campaign event where she was asked what prompted the Civil War. Her long-winded response avoided giving the answer to a basic question most learned in grade school, teeing up a barrage of criticism from political foes.