Nicole Gaudiano

USA TODAY

Libertarian presidential candidate Gary Johnson may have "blanked" this week when he asked an interviewer, "What is Aleppo?" But he was right when he said of such mental lapses, “It happens.” Other politicians have had their own Aleppo-esque moments.

Some other unforgettable examples of forgetfulness:

Rick Perry’s classic 'oops' moment

Perry, during a GOP presidential primary debate in 2011, struggled mightily — and painfully, for those watching — to name the three agencies he would abolish if elected president.

“Commerce, Education and the uh, what’s the third one there,” he said. He momentarily seized a lifeline when someone suggested the Environmental Protection Agency, but then quickly said EPA wasn’t the one — that agency only needed to be rebuilt.

The seconds dragged on before CNBC Moderator John Harwood asked, “You can’t name the third one?”

Perry gamely tried again: “I would do away with the Education, uh, the uh, Commerce and let’s see, I can’t, the third. Sorry. Oops.”

That elusive third agency, by the way, was the Energy Department.

Sarah Palin had trouble saying where she got her news

One of several low points for the 2008 vice presidential nominee during a multi-part interview with then-CBS Evening News anchor Katie Couric came when Couric asked what newspapers and magazines Palin regularly read to “stay informed and to understand the world.”

Palin began by answering “most” but fumbled as Couric pressed her for specifics.

“Um, all of 'em, any of 'em that, um, have, have been in front of me over all these years,” she said.

Pressed again for a name, she added, “I have a vast variety of sources where we get our news too. Alaska isn't a foreign country, where, it's kind of suggested, it seems like, 'Wow, how could you keep in touch with what the rest of Washington, D.C. may be thinking.”

Joe Biden’s mangling of Depression-era history

The vice president is known for many gaffes over the years, but this one offered double trouble:

“When the stock market crashed, Franklin D. Roosevelt got on the television and didn’t just talk about the, you know, the princes of greed. He said, ‘Look, here’s what happened,’” Biden told Couric in 2008.

Okay, except Franklin Roosevelt wasn’t president when the stock market crashed in 1929. And TVs were still in the experimental stage.

Dan Quayle and 'potatoe'-gate

We reach way back to 1992, because Vice President Dan Quayle’s misspelling of potato, like a hearty starch, has staying power. Quayle got fried in the media after telling a student, during a spelling bee, that the student's spelling of “potato” needed “one little bit on the end.”

OxfordWords Blog isn’t as hard on Quayle, given that “potato” was spelled with an “e” for almost the entire 20th century. But Quayle devoted a chapter of his memoir "Standing Firm" to the saga.

"It was a ‘defining moment’ of the worst kind imaginable,’’ he wrote.

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