Elon Musk has described US President Donald Trump's proposed spending bill as a "disgusting abomination" as tensions between the pair burst into the open following the tech billionaire's White House exit.
Mr Musk left his role as an official government employee last week, lauded by Mr Trump for spearheading a federal spending cuts programme, but disagreements between them have been building.
"This massive, outrageous, pork-filled Congressional spending bill is a disgusting abomination," Mr Musk posted on X, in by far his most caustic remarks on Mr Trump's spending plans.
"Shame on those who voted for it: you know you did wrong."
It was not Mr Musk's first comments on Mr Trump's so-called "big, beautiful bill" which is set to add $3 trillion to US deficits over a 10-year horizon, despite deep cuts to health and food aid programmes.
But Mr Musk's previous criticism was restrained, with the ex-head of Trump's Department of Government Efficiency (DOGE) task force offering only that it undermined his cost-cutting efforts.
He said that the bill - being considered by Congress - would burden "citizens with crushingly unsustainable debt."
The escalation in rhetoric indicated bitter hostilities between the White House and Mr Musk, who donated almost $300m to Mr Trump's election campaign but has recently voiced frustrations.
"The president already knows where Elon Musk stood on this bill, it doesn't change his opinion," White House Press Secretary Karoline Leavitt told reporters in a rapid response to Mr Musk's tweet.
"This is one big, beautiful bill, and he's sticking to it."
As the world's richest person bowed out of his role as Mr Trump's cost-cutter-in-chief, their relationship appeared on an even keel as the Republican hailed his fellow billionaire's "incredible service".
Once inseparable
Mr Trump even insisted that Mr Musk was "really not leaving" after a turbulent four months in which the South African born tycoon cut tens of thousands of jobs, shuttered whole agencies and slashed foreign aid.
Mr Musk was once almost inseparable from Mr Trump, glued to his side on Air Force One, Marine One, in the White House and at Trump's Mar-a-Lago resort in Florida.
But DOGE's achievements fell far short of Mr Musk's original goal of saving $2 trillion.
The DOGE website claims to have saved taxpayers about 8% of the $2 trillion figure so far - $175bn - and fact-checkers even see that claim as dubious, given previous serious inaccuracies in its accounting.
But the non-governmental "Musk Watch DOGE Tracker" puts the verifiable figure at $16bn - less than 1% of the goal.
Tesla shareholders called for Mr Musk to return to work as sales slumped and protests targeted the electric vehicle maker, while SpaceX had a series of rocket failures.
