WASHINGTON, United States (AFP) — Tensions between Elon Musk and Donald Trump erupted Tuesday as the world’s richest man derided the president’s key piece of economic legislation in a startling rupture just days after exiting a controversial job in the White House.

Musk was lauded by the Republican leader as he left his advisory role atop Trump’s “Department of Government Efficiency” (DoGE) last week, despite criticism over his failure to deliver on promises of radical spending cuts.

“This massive, outrageous, pork-filled Congressional spending bill is a disgusting abomination,” Musk posted on X as he followed its progress from the sidelines, in by far his most caustic remarks on Trump’s agenda.

“Shame on those who voted for it: you know you did wrong.”

It was not Musk’s first comments on 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 programs.

But Musk’s previous criticism was more restrained, with the Tesla and SpaceX magnate offering only that it undermined his cost-cutting efforts.

On Tuesday he said the bill — being considered by Congress — would burden “citizens with crushingly unsustainable debt.”

His post laid bare an increasingly tense relationship between the White House and Musk, who donated almost $300 million to Trump’s 2024 election campaign.

Musk has become disillusioned, US media reported, as his goals for White House action that would benefit him personally have gone unrealized.

The bill he was criticizing cuts the electric vehicle tax credit — bad news for Tesla — while Axios reported that Musk was rebuffed in his efforts to extend his role beyond the statutory 130-day limit.

He also failed to have his Starlink satellite system used for air traffic control, according to Axios, and was angered by Trump withdrawing the nomination of Musk ally Jared Isaacman to be NASA chief.