Gary Johnson just failed Foreign Policy 101 on live TV in a truly cringeworthy moment

Libertarian presidential nominee Gary Johnson inflicted serious harm on his already uphill battle to be taken seriously in the 2016 campaign Thursday morning, telling panelists on MSNBC's Morning Joe that he did not know why he should have a plan for Aleppo — the city at the heart of the Syrian civil war and refugee crisis.

"What would you do if you were elected about Aleppo?" Mike Barnicle, a regular on Morning Joe, asked Johnson.

"And what is Aleppo?" Johnson replied.

"You're kidding?" Barnicle answered back.

"No," Johnson said in response.

Aleppo has been at the forefront of Syria coverage for the better part of a year as the United States has debated what to do with the flow of refugees fleeing the war-torn city.

Just recently, an image of a boy in rescued from the streets of Aleppo covered in blood and dust went viral — sparking outrage about the human suffering in Syria.

Morning Joe panelists expressed astonishment at his answer after Johnson's appearance.

Twitter also pilloried Johnson.

And some said his complete lack of knowledge about one of the biggest ongoing foreign policy debates is an embarrassing moment that will likely haunt the rest of his bid.

In a statement given to the Daily Beast, Johnson said he "blanked" in the interview and apologized for the mistake, saying there are "many things I don't know off the top of my head."

But it's not clear that the apology will help Johnson with his most pressing and immediate challenge: reaching the 15% polling threshold needed to make the national debate stage in two weeks.

Hovering at around 9% in the RealClearPolitics average, that was already a monumental task. But his Aleppo blunder could almost certainly put that number out of reach.