India, Aug. 20 -- Senator Darline Graham stumbled visibly during a South Carolina Senate debate on Tuesday night, telling voters she was "not that informed on national security" when pressed on whether Taiwan and the South China Sea represent security concerns for the United States, deepening scrutiny of her readiness for a full six-year term just a week before a decisive Republican runoff.

Graham, who was appointed to the seat last month following the sudden death of her brother, Senator Lindsey Graham, faced the question from moderator Greta Van Susteren during the debate in Newberry, South Carolina, against her rival, Representative Ralph Norman. Her answer immediately drew comparisons to her brother's decades-long reputation as one o...