It was, in Gary Johnson’s own words, another “Aleppo moment.”

During a town hall-style interview on MSNBC on Wednesday night, Mr. Johnson, the Libertarian candidate for president, was asked by the host Chris Matthews to name his favorite foreign leader.

Mr. Johnson, appearing flustered, was at a loss to come up with a name.

He grasped at a former president of Mexico, Vicente Fox, who has been critical of Donald J. Trump, but was unable to remember his name without help — or the name of any sitting leader of a foreign country.

“I guess I’m having an Aleppo moment,” he said.

Mr. Johnson was referring to a remarkably similar episode earlier this month when, during another interview on MSNBC, he was asked how he would deal with the continuing situation in Aleppo, the ravaged Syrian city at the center of that country’s refugee crisis.