Washington DC - Joe Biden's pardon of his son Hunter has antagonized both sides of the US political divide, with Republicans crying hypocrisy and Democrats warning it undermines efforts to rein in Donald Trump.

Biden's announcement shocked Washington after he entered the White House in 2021 vowing to restore the "integrity" of a justice system that Democrats said had been corrupted by Trump – and because he had specifically vowed not to grant reprieve to his son.

The president instead issued a "full and unconditional" pardon on Sunday, absolving 54-year-old Hunter Biden of any wrongdoing over the last decade, charged or otherwise, just ahead of his looming sentencing over tax evasion and felony gun convictions.

Biden argued that his son had been targeted in a politicized prosecution launched under the Trump administration and that "there's no reason to believe it will stop here."

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But the backlash from his own side was swift.

"I know that there was a real strong sentiment and wanting to protect Hunter Biden from unfair prosecution," Glenn Ivey, a Democratic congressman in Maryland and an attorney, told CNN.

"But this is going to be used against us when we're fighting the misuses that are coming from the Trump administration."

While politicians typically pay lip service to the importance of independent law enforcement, Democrats and Republicans offer different justifications for suspicion of the Justice Department and presidents of both stripes have protected allies.

Trump wielded the pardon power liberally in favor of convicts with whom he had personal relationships, including his daughter's father-in-law Charles Kushner, his friend Roger Stone, and his 2016 campaign chairman Paul Manafort.

Meanwhile, Democrats worried that Trump would use Biden's action to justify pardoning rioters jailed after the January 6, 2021 assault on the US Capitol.

"Does the Pardon given by Joe to Hunter include the J-6 Hostages, who have now been imprisoned for years?" Trump wrote in a post on his platform, Truth Social, on Sunday. "Such an abuse and miscarriage of Justice!"

Democratic Colorado Governor Jared Polis said Biden's son had brought his legal woes on himself and accused the president of having "put his family ahead of the country."

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"This is a bad precedent that could be abused by later Presidents and will sadly tarnish his reputation," Polis posted on X. "When you become President, your role is Pater familias of the nation."

Political scientist Nicholas Creel, of Georgia College and State University argues however that nothing Biden does before leaving office will affect the actions of a successor who "simply does not care about precedent."

"Trump was never going to need an excuse to do whatever he wants once he takes office," he told AFP.

"So while I'm sure we'll get plenty of pundits claiming that Biden pardoning his son opens the door for Trump to use his pardon power in overtly personal and political ways, I find it laughable that this wasn't always going to be the case," Creel added.