Gary Johnson, the former New Mexico governor and Libertarian Party presidential nominee, revealed a surprising lack of foreign policy knowledge on Thursday that could rock his insurgent candidacy when he could not answer a basic question about the crisis in Aleppo, Syria.

“What is Aleppo?” Mr. Johnson said when asked on MSNBC how, as president, he would address the refugee crisis in the war-torn Syrian city.

When pressed as to whether he was serious, Mr. Johnson indicated that he really was not aware of the city, which has been widely covered during the years that Syria has been engulfed in civil war. After Mike Barnicle, an MSNBC commentator who is often part of the “Morning Joe” program panel, explained that Aleppo was the center of Syria’s refugee crisis, Mr. Johnson struggled to recover.