Former Vice President Joe Biden on Friday defended his rebuke of a voter in Iowa, whom he labeled a damn liar for accusing him of selling access to the White House.

The fact of the matter is, this guy stood up and he was, in fact, lying, the Democratic presidential candidate told NPR on the campaign bus to Decorah after the heated exchange went viral. I just pointed out, youre a liar. Its a fact. He lied, period.

On Thursday, Biden snapped at the 83-year-old retired farmer in New Hampton, who took the microphone at a campaign event to ask a question.

What ensued were allegations aimed at Biden over his sons past work on the board of Burisma Holdings, a Ukrainian energy firm. President Donald Trump and his allies chiefly attorney Rudy Giuliani have attempted to gin up suspicion of the matter as Biden, during his vice presidency, pushed for the ouster of ex-Ukrainian prosecutor general Viktor Shokin, who led a corruption investigation of Burisma.

There is no evidence of wrongdoing on the part of the Bidens, and Shokins firing had the support of the international community. Trumps request that Ukrainian President Volodymyr Zelensky investigate the family ultimately prompted House Democrats to launch an impeachment inquiry against him for potential power abuses.

Incensed by the voters remarks, which included a claim that Biden is too old to run for president, the candidate cut him off, seeming to comment on the voters physical appearance and stating, Im not sedentary, before challenging him to a fitness competition.

Lets do push-ups, he said. Lets run. Lets do whatever you want to do. Lets take an IQ test.

Maybe I shouldnt have kidded with him about that, Biden later conceded to NPR.

In a series of tweets on Thursday, Symone Sanders, Bidens senior adviser, denied that the former vice president said anything about the voters physicality, and inferred that she believed the Iowan heard the Burisma story on Fox News . She condemned the network for continuing to peddle the debunked conspiracy theories cooked up by Trump and Rudy Giuliani about Ukraine.

These lies will not go unchecked & well continue to lay out the facts, she said.