Former vice president Joe Biden on Thursday could not remember during which century the Obama administration took place, and also called a voter a "damn liar."

Speaking in New Hampton, Iowa, at a stop on his "No Malarkey" tour, Biden worked to recall the year the Obama administration signed an executive order, ending up with the year 1976.

"There's the Dreamers program, there's also a program that said we're not going to separate families, we're going to allow families to stay together while they go through the process, and the Court said you can't … We did that in 1976," he said.

"And, I mean—I'm sorry, excuse me," he added. "Backing up here—2014."

Things got heated at another point in the event when a voter asked Biden about his son Hunter's experience and qualifications to serve on the board of the Ukrainian gas giant Burisma.

"You, on the other hand, sent your son over there to get a job and work for a gas company that he had no experience—with gas or nothing—in order to get access to," the man told Biden. "So you are selling access to the president."

Biden raised his voice and approached the man, calling him a "damn liar." He even challenged him to a push-up contest.

"The reason I'm running is because I've been around a long time and I know more than most people know," Biden said, addressing the issue of his age. "And I can get things done, that's why I'm running, and if you want to check my shape, let's do push-ups man, let's run, let's do whatever you want to do. Let's take an IQ test."

WATCH: A tense exchange with a voter at ⁦@JoeBiden⁩’s event in New Hampton, IA this morning, where a voter started out by telling Biden he had two problems with him: he was too old, and his son’s work in Ukraine pic.twitter.com/ok7m0ShFPd — Molly Nagle (@MollyNagle3) December 5, 2019

The man also criticized President Donald Trump, and took a shot at Biden by likening his behavior to Trump's.

"It looks like you don't have any more backbone than Trump does," the man said.

Hunter Biden's place on the Burisma board has drawn scrutiny, with Trump even asking about it on a phone call with Ukrainian president Volodymyr Zelensky. That phone call is now at the center of the House of Representatives' impeachment inquiry, in which many congressional Democrats have alleged that Trump abused his power and violated his oath of office. Trump has denied these allegations.

This is not the first time Biden has punched back at a question by challenging someone to an IQ comparison. He did the same thing in 1988 when he ran for president and was asked about his performance in law school.