It was the most dramatic moment of Biden’s “No Malarkey” bus tour through Iowa and underscored the political landmines the Democratic candidate can encounter in unscripted moments on the campaign trail.

Biden has largely avoided talking about his son Hunter Biden’s work for the Ukrainian gas company Burisma — which dovetailed with the vice president’s portfolio in the country — after Trump repeatedly tried to pressure Ukraine into investigating the arrangement. Democrats are impeaching Trump for what they call an abuse his power.

But on Thursday in this small rural Iowa town, Biden couldn’t avoid the topic when the 83-year-old man said he had two problems with the 77-year-old Biden: his age and the Ukrainian issue.

“We all know Trump has been messing around in Ukraine,” the man said before pivoting to Biden.

“You on the other hand sent your son over there to get a job and work for a gas company and [who] had no experience in natural gas,” he said. “You’re selling access to the president just like he is.”

“You’re a damn liar, man. That’s not true. And no one has ever said that,” Biden interjected, walking up to him menacingly.

As the two talked over each other, a staffer tried to take the man’s microphone. But Biden waved him away and let the man keep the mic.

“Let him go. Let him go,” Biden said. He said that “the reason I’m running is because I’ve been around a long time and I know more than most people now and I can get things done. And that’s why I’m running.”

Returning to the issue of his age and fitness, Biden then laid down the challenge: “Let’s do push-ups together here, man. Let’s run. Let’s do whatever you want to do. Let’s take an IQ test.”

The man was speechless.

“No one has said my son has done anything wrong,” Biden said, adding that he “did not on any occasion” do anything wrong and that “no one has ever said it.”

“I didn’t say you were doing anything wrong,” the man replied.

“You said I set up my son to work on an oil company,” Biden shot back. “Isn’t that what you said? Get your words straight, Jack!

The man said he heard it on MSNBC, at which point Biden yelled again.

“You don’t hear that on MSNBC! You did not hear that at all,” Biden said. “Look, I’m not going to get into an argument with you man.”

At one point, Biden appeared to call the man “fat” by mistake. That’s when the man got in a dig.

“You don’t have any more backbone than Trump does,” he said.

The crowd booed him.

“Any other questions?” Biden said, looking to others.

“Wel,l I’m not voting for you,” the man said.

“Well, I knew you weren’t,” Biden said. “You’re too old to vote for me.”

The crowd cheered. The man sat down and Biden moved on.