Hunter Biden's history of controversial business deals, drugs and women has long made him a target for the elder Biden's Republican enemies.
That culminated in the opening of a House impeachment inquiry against the president on Tuesday.
But if some see Hunter as the black sheep of America's first family, the 80-year-old Joe Biden has resolutely stood by his sole surviving son, against a backdrop of tragedy.
"My son's done nothing wrong. I trust him. I have faith in him," Biden said in an interview earlier this year about tax and gun charges against the 53-year-old Hunter.
Asked how Hunter's problems could affect his presidency, Biden replied: "It impacts my presidency by making me proud of him."
Yet while Biden's love has been unwavering, Hunter's woes show no sign of fading.
In fact, the impeachment probe looking at whether Biden lied about his son's business deals in Ukraine and China threaten to create a bigger headache than ever for the White House ahead of next year's election.
The Bidens' bond was forged through terrible loss.
A car crash in 1972 killed Hunter's mother Neilia and baby sister Naomi, left two-year-old Hunter with a fractured skull and his older brother Beau with multiple broken bones.
"The pain had seemed unbearable in the beginning," Joe Biden wrote in his 2017 memoir "Promise Me, Dad."
He was sworn in as a newly-elected senator by Hunter and Beau's hospital bedside and it was just the three of them until he met his second wife, Jill.
"They'd always been there for each other, from the time they were little boys," Biden wrote.
Yet Hunter also lived in the shadow of Beau, who had a sterling military career and went into politics, with Biden imagining Beau might one day be president.
A graduate of Yale law school, Hunter drifted between jobs in government, banking and lobbying before landing in a family-controlled hedge fund and his own international business consultancy in the late 2000s.
His life became increasingly marred by alcoholism and addiction to crack cocaine. In 2014 he was discharged from the Navy Reserve after a positive test for cocaine.
Things worsened drastically after his brother died from brain cancer in 2015, aged 46.
"After Beau died, I never felt more alone. I lost hope," he wrote in his 2021 memoir "Beautiful Things."
His marriage crumbled and he lost custody of his three daughters. His ex-wife Kathleen Buhle said in her memoir his addictions spiraled and he racked up bills for strip clubs and liquor stores.
Hunter then had an affair with Beau's widow and had a daughter with a woman in Arkansas whom Joe Biden only recently publicly acknowledged as his seventh grandchild.
Then he saw his files, emails and lurid photos from his laptop computer made public by his father's enemies, as they alleged a toxic brew of nepotism between Joe Biden and his son.
Despite all that, the teetotal Joe Biden has always defended Hunter.
"My son, like a lot of people... had a drug problem," Biden said when Donald Trump raised Hunter's drug use and business deals during a TV debate in the 2020 presidential race.
Hunter said he'd been clean since 2019 following an intervention by his second wife Melissa -- with whom he had a son, Beau -- and his father.
"He never abandoned me, never shunned me, never judged me, no matter how bad things got," Hunter wrote.
"There were times when his persistence infuriated me -- I'd attempt to fade to black through alcoholism or drug addiction, and then there he was, barging in again with his lantern, shining a light, disrupting my plans to disappear," he said.
He took up painting -- though that brought fresh controversy when unnamed collectors bought his works for prices in the hundreds of thousands of dollars.
Biden has kept his son close this year, taking him to Ireland in April and hosting him on the White House balcony for Independence Day celebrations.
But the New York Times last week quoted unidentified Biden allies as saying that doing so "has resulted in wholly avoidable political distractions."
