Former Vice President Joe Biden has surprised many by calling a 21-year-old student a “lying, dog-faced pony soldier” at a campaign event, after she questioned him about his poor showing in the Iowa caucus.

Madison Moore had pre-warned the democratic candidate she wouldn't be fielding an easy question, ahead of asking Mr Biden: “How do you explain the performance in Iowa and why should the voters believe that you can win a national election?".

Mr Biden, 77, responded by asking "Iowa’s a caucus. Have you ever been to a caucus?” before throwing out the bizarre remark.

"No, you haven’t. You’re a lying, dog-faced pony soldier," he said, when Ms Moore indicated she had.

Social media went into overdrive after footage of the exchange emerged.

Hillary called us a "basket of deplorables." Joe Biden called us "dog-faced pony soldiers."



I know what a deplorable is. What the hell is a dog-faced pony soldier? — Bill Mitchell (@mitchellvii) February 10, 2020

Please stop picking on poor elderly @JoeBiden. This is what he actually meant.

#LyingDogFacedPonySoldier pic.twitter.com/AFmTuTDr84 — R. L. Patton (@PCTGeneral) February 9, 2020

Some declared it was officially the end of Mr Biden’s campaign, even calling on the former vice president to quit.

On Sunday, Joe Biden called a voter in New Hampshire, a “lying, dog-faced pony soldier.” I assume that's the official end of the Biden 2020 campaign. am I right? Well, there's always 2024, #LyingDogFacedPonySoldier https://t.co/TPHKkzHbU5 — Rob Barrett Jr. for Senate (@RobSenate) February 10, 2020

Are we still pretending that Joe Biden hasn’t lost his marbles?



Do yourselves and Google a video of him from 30 years ago and compare it to him now and tell me it’s the same person! Long gone. https://t.co/FLpocHkEJv — Donald Trump Jr. (@DonaldJTrumpJr) February 9, 2020

Unknown to many, this is not the first time Mr Biden has used the phrase.

In 2018 at a Heidi Keitkamp campaign event, Mr Biden described her opponent, Kevin Cramer, using the same phrase - one he attributes to a John Wayne movie.

“As my brother, who loves to use lines from movies, from John Wayne movies, there’s a line in a movie, a John Wayne movie where an Indian chief turns to John Wayne and says, 'This is a lying, dog-faced pony soldier',” Mr Biden said.

The obscure nature of the line led to Mr Biden’s campaign team reiterating it was a joke on social media.

Like Olivia notes, it's a joke that was met with.... drumroll... laughter in the room and from the questioner. It's from a John Wayne movie and he's made it plenty of times before. Sorry to ruin the fun twitter! https://t.co/XIbn8wF53W https://t.co/5D0Kk06RGK — Remi Yamamoto (@RemiMYamamoto) February 9, 2020

Mr Biden did go on to tell the student her question wasn’t “hard” but “honest”.

“It was a little bit confusing in Iowa, number one," he said, referencing the chaotic and delayed results.

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"Let's assume it was all, everything was exactly right in Iowa. The idea that you come in with half the delegates the leaders come in with in Iowa doesn't necessarily say how you’re going to win Michigan, how you’re going to win Pennsylvania," he said.

Mr Biden came in fourth in the Iowa caucus with just over 10 per cent of the vote.