Ben Carson’s remarks on foreign policy have repeatedly raised questions about his grasp of the subject, but never more seriously than in the past week, when he wrongly asserted that China had intervened militarily in Syria and then failed, on national television, to name the countries he would call on to form a coalition to fight the Islamic State.

Faced with increasing scrutiny about whether Mr. Carson, who leads in some Republican presidential polls, was capable of leading American foreign policy, two of his top advisers said in interviews that he had struggled to master the intricacies of the Middle East and national security and that intense tutoring was having little effect.

“Nobody has been able to sit down with him and have him get one iota of intelligent information about the Middle East,” said Duane R. Clarridge, a top adviser to Mr. Carson on terrorism and national security. He also said Mr. Carson needed weekly conference calls briefing him on foreign policy so “we can make him smart.”

As the deadly assaults in Paris claimed by the Islamic State reframe the presidential race, the candidates’ foreign policy credentials are suddenly under scrutiny. And Mr. Carson has attracted extra attention because his statements give rise to questions about where, as a retired neurosurgeon without government experience, he turns for information and counsel on complex global issues. What is unusual is the candor of those who are tutoring him about his struggle to master the subject.