(CNN) Libertarian presidential nominee Gary Johnson stumbled while answering a question about the Syrian refugee crisis on Thursday, asking " What is Aleppo ?" in an interview on MSNBC.

"About?" Johnson said.

"Aleppo," Barnicle responded.

Johnson paused and said: "And what is Aleppo?"

"You're kidding ..." the incredulous Barnicle answered.

"No," Johnson said.

"Aleppo is in Syria -- it's the epicenter of the refugee crisis," Barnicle said.

"OK. Got it. With regard to Syria, I do think it is a mess," the Libertarian nominee said.

Johnson pivoted to arguing against military interventions in foreign countries, and said that the refugee crisis "is the result of regime change that we end up supporting, and, inevitably, these regimes have led to a less safe world."

He also suggested that the US should "join hands with Russia" to bring an end to the conflict in Syria.

Host Joe Scarborough, though, pressed Johnson on his confusion about Aleppo.

Photos: Aleppo photographer watches city die Photos: Aleppo photographer watches city die Two children walk past a "White Helmet" soon after an airstrike hits the Shaar neighborhood of Aleppo. Hide Caption 1 of 10 Photos: Aleppo photographer watches city die Members of the "White Helmets" civil defense volunteers carry the body of a man killed in a Russian airstrike in Andan town in the countryside north of of Aleppo. Hide Caption 2 of 10 Photos: Aleppo photographer watches city die Buses piled one on top of the other offer some protection from enemy fire. Hide Caption 3 of 10 Photos: Aleppo photographer watches city die Keeping the lights on: The electricity "operations room" in a neighborhood of rebel-held Aleppo. Hide Caption 4 of 10 Photos: Aleppo photographer watches city die Two men and their donkey navigate the bombed alleyways of Almarja district in eastern Aleppo. Hide Caption 5 of 10 Photos: Aleppo photographer watches city die A mother watches over her children as they return from school; the massive sheet hanging in the street is to deter government snipers. Hide Caption 6 of 10 Photos: Aleppo photographer watches city die A street that is monitored by regime snipers. Hide Caption 7 of 10 Photos: Aleppo photographer watches city die A stall holder waits for customers; there are reports of some hoarding of rice and flour as the regime's siege tightens. Hide Caption 8 of 10 Photos: Aleppo photographer watches city die A street market in Aleppo that is still open despite constant airstrikes -- and the huge slab of concrete hanging over it. Hide Caption 9 of 10 Photos: Aleppo photographer watches city die There is still fresh produce in the market stalls but it is more difficult to bring into the city, and much more expensive than even a few weeks ago. Hide Caption 10 of 10

"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. You asked, 'What is Aleppo?' Do you really think that foreign policy is so insignificant that somebody who is running for president of the United States shouldn't even know what Aleppo is, where Aleppo is, and why it is so important?" he asked.

Johnson answered: "Well, no, 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 with a situation that in most cases is not better. And in many cases ends up being worse."

In a follow up interview just after the show with Bloomberg News' Mark Halperin, a frequent guest analyst on "Morning Joe," Johnson said he was "incredibly frustrated" with himsself but admitted he'd been caught flat-footed.

"Not remembering or identifying that that's Aleppo -- guilty," he said. "I understand the significance. Genuinely -- believe me, no one is taking this more seriously than me. I feel horrible."

He added: "I have to get smarter, and that's just part of the process."

Johnson later issued an unconventional press statement that sought to explain, in great detail, his error and to brace his supporters for mistakes to come:

This morning, I began my day by setting aside any doubt that I'm human. Yes, I understand the dynamics of the Syrian conflict -- I talk about them every day. But hit with 'What about Aleppo?', I immediately was thinking about an acronym, not the Syrian conflict. I blanked. It happens, and it will happen again during the course of this campaign.

Can I name every city in Syria? No. Should I have identified Aleppo? Yes. Do I understand its significance? Yes.

As Governor, there were many things I didn't know off the top of my head. But I succeeded by surrounding myself with the right people, getting to the bottom of important issues, and making principled decisions. It worked. That is what a President must do.

That would begin, clearly, with daily security briefings that, to me, will be fundamental to the job of being President.

Hillary Clinton swiped at Johnson for the gaffe when she was asked about his stumble during a news conference early Thursday.

"Well, you could look on a map and find Aleppo," she said.

Later, during an appearance on ABC's "The View," Johnson continued to address the gaffe.

"There's no excuse. I was thinking in terms of an acronym - Aleppo," he explained. Johnson also said he thought the question was a fair one since he's running for president.

Co-host Joy Behar told Johnson, "I think it's a disqualifying statement, frankly."

"Fair enough. Fair enough," Johnson replied.