President Joe Biden's silence spoke volumes on Friday after his son Hunter's legal woes deepened with lurid allegations that he avoided paying taxes while spending millions on drugs and escorts.

The 81-year-old president has long defended Hunter, even though the second set of federal charges against his troubled son are a fresh embarrassment ahead of an uphill battle to be reelected in 2024.

As Hunter Biden, 53, said in an interview released Friday that Republicans were trying to "kill me" to destroy the Democrat's presidency, the elder Biden's approach was to stonewall questions instead.

Wearing his trademark aviator sunglasses, the president waved to reporters but ignored questions as he boarded his Marine One helicopter at the White House. 

The often garrulous Biden did the same thing as he boarded Air Force One for a trip to Las Vegas, where he will unveil major rail investments as he tries to convince skeptical voters that his economic renewal policies are working. 

Biden is heading for a likely rematch with Donald Trump next year, and is also fending off a Republican bid to impeach him on grounds that he benefited from his son's overseas business dealings in Ukraine and China.

'Loves his son'

The White House, however, was clear about the message.

"The president has said this before, and he will continue to say it, which is that he loves his son and supports him as he continues to rebuild his life," Press Secretary Karine Jean-Pierre told reporters aboard the presidential jet.

"He's proud of his son." 

Hunter Biden is a Yale-trained lawyer and lobbyist-turned-artist, but his life has been marred by alcoholism and crack cocaine addiction.

He was indicted on multiple counts on Thursday of evading at least $1.4 million in tax between 2016 and 2020, the second time he has been charged by a special counsel investigating his personal and business dealings.

"The defendant spent millions of dollars on an extravagant lifestyle at the same time he chose not to pay his taxes," special counsel David Weiss said in the indictment.

Hunter Biden "spent this money on drugs, escorts and girlfriends, luxury hotels and rental properties, exotic cars, clothing, and other items of a personal nature, in short, everything but his taxes," it said.

The indictment says Hunter Biden earned more than $7 million during the period and made $1.6 million in ATM withdrawals, spent $683,212 on payments to "various women" and $188,960 on "adult entertainment".

His attorney Abbe Lowell said in a statement in US media that he had paid his taxes in full.

If Hunter's "last name was anything other than Biden, the charges in Delaware, and now California, would not have been brought," the attorney added.

The previous charges in Delaware accuse Hunter Biden of lying about his drug use when he purchased a gun.

'Trying to kill me'

In a podcast with musician Moby recorded before the charges were unveiled, Hunter Biden said he was being harassed by rightwingers who wanted to drive him back into addiction.

"They're trying to destroy a presidency. And so it's not about me," he told Moby, a fierce critic of Trump, in the interview released Friday.

"And their most base way what they're trying to do, they're trying to kill me, knowing it will be a pain greater than my father could be able to handle."

Trailing Trump in the polls and caught in two grinding wars involving US allies Israel and Ukraine, Biden could do without the fresh ammunition that the Hunter charges will give Republicans.

The charges are especially embarrassing as Biden often rails about the rich not paying enough tax.

But Biden has always steadfastly defended his son, pointing to the long history of tragedy that has dogged the family. 

Hunter Biden's mother and sister were killed in a 1972 car crash. Hunter, who was two at the time, and his older brother Beau were badly injured.

His brother died from brain cancer in 2015, aged 46.

"When Beau died I just completely unraveled. It's not an excuse, but it is the reason," he told Moby.

The family's unity was on display in November when father and son — and grandson "Baby Beau", aged three — were seen visiting the island of Nantucket together for the Thanksgiving holiday.