Former New Mexico Gov. Gary Johnson in an interview with MSNBC. MSNBC

Call it a "Tubman moment."

Gary Johnson, the gaffe-prone Libertarian Party candidate for president, seemingly has a tendency to forget things.

Months before Johnson failed to recall what Aleppo is — Syria's largest city, and one of the hardest hit by the ongoing civil war — during an interview with MSNBC, he apparently had to ask an aide who Harriet Tubman was.

The nugget is buried in a long New Yorker profile from July about Johnson's third-party candidacy for the White House.

After giving a speech at a Libertarian political convention in California, Johnson was questioned whether diversity was "a problem" for the Libertarian Party, which is mostly young, white, and male.

He responded that his party would start doing better among nonwhite voters once he became more nationally recognized.

Shortly thereafter, Johnson was shepherded into a room at the convention center that was named after Harriet Tubman.

"Who's Harriet Tubman?" Johnson asked an aide, according to The New Yorker. The aide had to quietly remind Johnson who Tubman was.

Harriet Tubman on the new $20 bill. Women on 20s

Tubman, of course, is an American civil rights icon. Born into slavery, she served as an armed scout for the Union during the Civil War and fought for women's suffrage. Tubman's face will grace the newest iteration of the $20 bill.

But clearly, that wasn't the end of Johnson's troubles.

On Wednesday, Johnson admitted to MSNBC's Chris Matthews he was having an "Aleppo moment" when he couldn't immediately name any foreign leaders he respected.

He doubled down on his inability to name any foreign leaders in a tweet on Thursday, saying, "It's been almost 24 hours... and I still can't come up with a foreign leader I look up to."

While Johnson has had some trouble getting his poll numbers up to a comfortable level, The Chicago Tribune endorsed him for president on Friday.

Johnson's campaign wasn't immediately available for comment.