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

"What is Aleppo?" Johnson said when asked on MSNBC how, as president, he would address the refugee crisis in the Syrian city that is the de facto capital of the Islamic State in Iraq and the Levant.

"You're kidding," replied "Morning Joe" regular guest Mike Barnicle.

When pressed as to whether he was serious, 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, Johnson struggled to recover.

"OK, got it," he said, explaining that he thinks that the United States must partner with Russia to diplomatically improve the situation there. "With regard to Syria, I do think that it's a mess."

Host Joe Scarborough pressed Johnson on his whiff.

"So Aleppo is the center of a lot of people's concerns across the planet about the terrible humanitarian crisis that is unfolding not only in Syria, but especially in Aleppo," Scarborough said. "You asked, 'What is Aleppo?' Do you really think that foreign policy is so insignificant that somebody running for president of the United States shouldn't even know what Aleppo is, where Aleppo is, why Aleppo is so important?"

"No," replied Johnson, who is a noninterventionist. "I do understand Aleppo and I … understand the crisis that is going on. But when we involve ourselves militarily, when we involve ourselves in these humanitarian issues, we end up — we end up with a situation that in most cases is not better, and in many cases ends up being worse."

The stumble could be a serious blow to Johnson's campaign, just as he is making a final push to improve his standing in the polls. His support needs to reach 15 percent in a series of major national polls to be included in the presidential debates.

Johnson's support has been hovering around 10 percent. He and his running mate, former Gov. Bill Weld of Massachusetts, have been aggressively making the case that they represent a viable alternative for voters who are not happy with the major party nominees Hillary Clinton and Donald Trump.

Johnson and Weld are both former two-term Republican governors who are socially liberal and fiscally conservative.

Some leading Republicans who oppose Trump have said openly that they are giving the Libertarian ticket a serious look. On Wednesday night, Mitt Romney, the 2012 Republican nominee, publicly called for Johnson and Weld to be included in the presidential debates.

The stumble was widely mocked on social media, and on Twitter the question "What is Aleppo?" was trending.

Johnson expressed disappointment about the lapse in a brief follow-up interview that was broadcast on MSNBC.

"I'm incredibly frustrated with myself," he said.

The Washington Post contributed to this report.