Former US president Joe Biden has hit out at his successor Donald Trump's frenetic government overhaul, claiming the "hatchet" effort put Americans' retirement benefits at risk.
Mr Biden's address to disability advocates in Chicago, his first major speech since leaving the White House, marked a major re-emergence onto the US's political landscape.
It comes as Mr Trump's Department of Government Efficiency, run by tech billionaire Elon Musk, makes massive cuts to the federal workforce.
Mr Biden said the Trump administration has "taken a hatchet" to the the Social Security Administration.
"This new administration has done so much damage and so much destruction," he said, as he called Social Security "more than a government programme."
"It's a sacred promise we made as a nation. We know just how much Social Security matters to people's lives."
The SSA pays out $1.4 trillion in benefits to 73 million elderly and disabled Americans annually. Mr Trump repeatedly pledged during his election campaign not to touch Social Security benefits.
Watch: Former US president Joe Biden says Trump administration has 'taken a hatchet' to Social Security
Members of the DOGE team have been inside the agency since February, where leadership has pledged to cut at least 7,000 staff and close offices, triggering fears of longer lines, longer wait times and benefit disruptions.
In March a federal judge said the SSA likely violated privacy laws by giving Mr Musk's aides "unbridled access" to the data of millions of Americans inside the agency's networks, and ordered a temporary halt to further record-sharing. The case continues.
"President Trump is absolutely certain about protecting Social Security benefits for law-abiding tax-paying American citizens and seniors who have paid into this programme. He will always protect that programme," Karoline Leavitt, Mr Trump's press secretary, told reporters before Mr Biden's speech.
Many layoffs or resignations have taken place inside the agency's IT departments, and Mr Biden referred to a recent increase in the number of times the agency's computer systems have crashed.
"People can't sign on to their accounts," Mr Biden said. "Who in the hell do they think they are?" he said of the Trump administration.
Some Democrats had misgivings about Mr Biden’s speech, saying it might be better for him not to re-enter the political fray.
Karen Finney, a Democratic strategist, said many Democrats are concerned that Mr Biden’s appearance will distract from the political and economic blowback Mr Trump is getting for triggering a trade war with China and imposing tariffs on other countries.
"We are finally beginning to see cracks in the armour in terms of Trump’s policies," Ms Finney said.
"You don’t want to become a lightning rod that distracts from Trump. And it could make it easy for Trump to change the subject to Biden."
Mr Biden, 82, dropped his re-election bid last July after a poor debate performance against Mr Trump.
Kamala Harris, his vice president, then lost the November election.
Mr Biden left office in January with one of the lowest approval ratings for a post-World War II president, at 38%, according to a Reuters/Ipsos opinion poll, and after a four-year term marked by high inflation and questions about his mental acuity.
Many Democrats blamed him for Mr Trump's victory.
However presidential historian Timothy Naftali said it was important for Mr Biden to speak out about Social Security, precisely because of his age.
"I understand why some Democrats would like Biden to fade away," Mr Naftali said.
"But a very important part of the Democratic base remains older people on Social Security, and Joe Biden has always been their champion."
