(CNN) Joe Biden's feisty exchange with a retired Iowa farmer on Thursday perfectly captured the perils and the potential of his candidacy.

In a human moment defending his son, Biden showed the authenticity, emotion and readiness for a fight that appeals to so many Democrats as they look for someone who can take on Trump.

At the same time, the elder statesman who is supposed to be the antidote to President Donald Trump was undisciplined and undeniably macho -- reminding voters he's an at times undisciplined contender who almost seemed ready for fisticuffs with a hostile questioner.

Thursday afternoon's exchange could benefit Biden at a time when Democrats say toughness is one of their most coveted assets in their battle against Trump.

It could help Biden allay the doubts of Democratic voters who have continually complained in interviews that the former vice president is too soft-spoken; too slow compared to his pace in the 2008 and 2012 campaigns; and too flat-footed when attacked during debates by the likes of Kamala Harris and Julián Castro

Though most political consultants would counsel their candidates not to personally attack voters as Biden did Thursday, he at least looked like he wouldn't shy away from the fight.

At a deeper level, Biden knows that one of his biggest challenges is the relentless effort by President Donald Trump, Rudy Giuliani and other Republican leaders to falsely define him as some kind of corrupt operator who sought lucrative gigs for his son in Ukraine.

Trump has shown a unique talent for that kind of attack on his opponents. One needs to look no further than the field of fallen 2016 GOP candidates and his relentless jibes against "crooked" Hillary Clinton and her missing emails to see the damage he can inflict.

As much as Biden has tried to avoid getting tangled up in Ukraine conspiracy theories, GOP members mentioned Joe and Hunter Biden countless times during the impeachment hearings on Ukraine, leaving some Americans confused about the Bidens' ties to the controversy. Clarity in squelching unsubstantiated charges will be key to whether Biden can survive.

He was easily provoked Thursday because the retired farmer who confronted him essentially outlined Trump's false accusations against the former vice president.

The exchange unfolded at a town hall in New Hampton, Iowa, on Thursday afternoon when Biden's 83-year-old adversary inaccurately accused of the former vice president of arranging a job for his son Hunter at a Ukraine oil company, thereby "selling access to the presidency," and punctuated his charges by asserting Biden was just "too old" to be commander in chief.

"You're a damn liar man," Biden said, addressing the allegation about Hunter with a flash of anger in his eyes. "That's not true and no one has ever said that."

He answered the man's attack on his age and his mental agility by showing the streak of unvarnished masculinity that has long been part of Biden's public persona.

"You want to check my shape -- let's do push-ups together man. Let's run, let's do whatever you want to do," Biden said.

The mano-a-mano moment was reminiscent of Biden's exchange during his 1988 campaign with New Hampshire voter Frank Fahey who asked Biden where he went to law school and what his class rank was.

"I think I probably have a much higher IQ than you do, I suspect. I went to law school on a full academic scholarship," the then-Delaware senator replied. "I'd be delighted to sit down and compare my IQ to yours if you'd like."

It also had the red-blooded ring of Biden's challenge to Trump when he said in March 2018 that if he and Trump were in high school "I'd take him behind the gym and beat the hell out of him."

It's an open question how Biden's machismo will go over with suburban women looking to turn the page beyond the patriarchy. And Biden's approach could turn off younger voters and female voters who want to the Democratic Party go in a more progressive direction and build on the gains of the many female leaders at all levels of government who were elected in 2018.

Biden's reaction on Thursday also clearly stemmed from his sensitivity to criticism of his family, a through line throughout his career.

After defending his own fitness for the White House, Biden circled back to defend his son, who served on the board of the Ukraine energy company known as Burisma while Biden was vice president. Hunter Biden recently told ABC that he showed "poor judgment" by taking the post. There is no evidence of wrongdoing by either Biden, however.

The retired Iowa farmer had pushed back on Biden's denials of helping Hunter Biden by saying he'd seen the arrangement described on TV, adding that he wasn't accusing Biden of anything.

"You said I set up my son to work at an oil company. Isn't that what you said? Get your words straight, Jack," the former vice president said to the retired farmer. "You did not hear that at all."

"It looks like you don't have any more backbone than Trump has," the man replied, as the rest of the audience groaned. "I'm not voting for you anyway."

"You think I thought you'd stand up and vote for me," Biden snapped. "You're too old to vote for me." (Again, probably not the smartest thing to say to a voter -- but authentically "Joe.")

After the event, when reporters asked Biden why he got so frustrated with the retired farmer, the former vice president acknowledged his competing instincts to defend his son or play it cool.

"I have overwhelming respect and love for my son. And I find myself occasionally getting frustrated with assertions that have been made -- that are simply not accurate," Biden said. "But as my son would say, 'Dad, just keep your cool, just don't let it get to you.'"

"What I wanted to do is shut this down," Biden said, reflecting on his effort to avoid playing Trump's "game" and his realization that the President is most "comfortable mud wrestling."

"Let's keep our eye on the ball here," he said. As for the voter who served as his antagonist Thursday, a reporter told Biden the retired farmer acknowledged he'll vote for the former vice president if he becomes the Democratic nominee.

"Well, God love him," Biden replied. "Big heart."