US First Lady Jill Biden slammed Republican attacks on her troubled son Hunter and blasted Donald Trump as a threat to democracy as she came out swinging for her husbands reelection campaign Thursday.

I think what they are doing to Hunter is cruel, Jill Biden told MSNBCs Morning Joe talk show in a rare public defense of Hunter. And Im really proud of how Hunter has rebuilt his life after addiction.

The 72-year-old teacher has been taking an increasingly prominent and vocal role in her husbands campaign for a second term, in which he faces a likely rematch with Trump.

But it remains unusual for her to touch on personal matters like Hunter Biden, who has been targeted by Republicans over his drug problems and legal woes as they try to inflict damage on the Democratic president ahead of Novembers vote.

The interview aired a day after a chaotic Congressional hearing during which one Republican lawmaker showed explicit pictures of Hunter Biden and another accused him of having no balls.

You know, I love my son. And its hurt my grandchildren, and thats what Im so concerned about that. Its affecting their lives as well, she said of the Republican attacks.

Hunter Biden also faces federal tax charges, for which he was due to appear in court in Los Angeles on Thursday, and gun charges.

He made a surprise appearance Wednesday on Capitol Hill as two Republican-led House committees gathered to debate contempt resolutions, after he defied their subpoenas for closed-door testimony.

˜See his vigor

Joe Biden has always strongly defended his only surviving son, whose mother and sister died in a car crash when Hunter was a toddler - Biden later married Jill.

Hunter Bidens older brother Beau died of brain cancer in 2015.

Jill Biden laughed when asked about Republicans who branded them a Biden crime family during the hearing.

Look at what the other sides, the extremists, have turned this country into. I mean, we would never see things like that, say, 10 years ago, she said.

The US first lady then strongly defended her husband against concerns over his age - he is already Americas oldest ever president and would be 86 at the end of a second term.

Polls show it is a major concern with voters, with recent surveys putting Biden neck-and-neck with or behind Trump.

I see his vigor, I see his energy, I see his passion every single day, she said.

I say his age is an asset - hes wise. He has experience. He knows every leader on the world stage. Hes lived history. He knows history.

Jill Biden went on to criticize Trump, particularly for describing as hostages the rioters who have been jailed for the January 6, 2021 assault on the US Capitol by Trump supporters trying to overturn Bidens election.

He doesnt call them what they were - insurrectionists, dangerous extremists, she said in the interview with Morning Joe co-host Mika Brzezinski.

That makes me want to be in the fight even more because we have to win¦ we cannot let go of our democracy, she said.

The choice of Brzezinski also sent a message as Trump repeatedly targeted the journalist while in office, describing her as Crazy Mika and spreading a false conspiracy theory about her co-host Joe Scarborough, whom he dubbed Psycho Joe. (AFP)