(NEW HAMPTON, IA) — In a strikingly tense moment on the campaign trail, Joe Biden confronted a man at a town hall in New Hampton, Iowa, calling him “a damn liar” after he pressed the former vice president on his son’s business ties to Ukraine.”We all know Trump has been messing around in Ukraine over there, saying that they want to investigate you. He has no backbone, we know that. But 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 for the president. So you’re selling access to the president just like he was,” the man told Biden, after saying Biden was too old to be president. “You’re a damn liar, man. That’s not true. No one has ever said that,” a heated Biden responded. “No one has said my son has done anything wrong, and I did not on any occasion, and nobody has ever said it.”Biden also challenged the man to do push-ups and take an IQ test with him to prove his physical and mental fitness to be president.xAfter the man, who refused to give his name to ABC News, said he is not voting for Biden, the presidential contender and front-runner said, “Of course you’re not. You’re too old to vote for me.”At the heart of the man’s allegations against Biden and his son, Hunter, is that the younger Biden accepted a lucrative seat on the board of directors for Burisma, the Ukrainian company in 2014, during the elder Biden’s tenure as vice president.While the Bidens have not been accused of doing anything illegal, ethics experts say Hunter Biden’s foreign business activity presents ethical concerns.This is not the first time Biden, who has previously launched unsuccessful bids for nation’s highest office in 1988 and 2008, engaged in a tense exchange with an attendee at a campaign event. During Biden’s first run for president in 1987, a New Hampshire voter, Frank Fahey, found himself on the receiving end of a tirade from the former Delaware senator after he asked what he thought was an innocent question about Biden’s law school experience.Biden took the question as an insult and partially responded, “I think I probably have a much higher IQ than you do, I suspect. I went to law school on a full academic scholarship.”Last month, Fahey, who is now supporting Biden for president and called him the best candidate for the job, reminded Biden of the exchange in early November in New London, and asked Biden what he would have done differently in his handling of the Anita Hill hearings during Clarence Thomas’ Supreme Court confirmation hearing.”You ask all the easy questions…Frankie, baby, it’s no wonder I love you,” Biden joked initially before saying he did all he could to help Hill under the rules of the committee at the time, but admitted that she was treated unfairly. Copyright © 2019, ABC Audio. All rights reserved.