'Get your words straight!': Biden spars with Iowa voter

"You're a damn liar, man," an agitated Biden told a man at a campaign event in New Hampton, Iowa, who suggested that Biden had helped his son Hunter land a lucrative position with the Ukrainian oil company Burisma.

"No one has said my son has done anything wrong," Biden told the man, who did not identify himself. "Get your words straight, jack."

Trump's push to suggest that Biden, as vice president, worked to aid Hunter Biden's business activities in Ukraine, is at the center of the impeachment inquiry being conducted by the U.S. House of Representatives. Trump and his allies have offered no evidence to support that claim.

The heckler at the Iowa event also questioned Biden's fitness for office. The 77-year-old former vice president responded by challenging the man to a push-up contest or an IQ test and at one point appeared to call him "fat."

Trump's re-election campaign quickly posted the video of the exchange, suggesting that Biden had gone "berserk."

Biden was in New Hampton as part of his eight-day bus tour across Iowa as he seeks to secure his place as one of the leading contenders for the Democratic presidential nomination. The exchange was part of what had already been an eventful day for the candidate.

His campaign drew widespread praise on social media for a Twitter video post late Wednesday in which Biden called Trump a laughingstock among world leaders. By mid-day Thursday it had been viewed on Twitter 8 million times.