The sudden fallout ended a nearly yearlong partnership, during which Mr. Musk helped propel Mr. Trump to the White House and became one of the president’s top advisers.
It was always the most unlikely of alliances.
Last year, two mercurial billionaires formed a partnership and vowed to drive the country in a new direction. Donald Trump had the political power. Elon Musk had the money and social media might.
But on Thursday, their union dissolved in remarkably public and rapid fashion, with the two men attacking each other over matters both significant and petty.
Beyond the immediate drama, the breakup of the president and the world’s richest man upended one of the most powerful dynamics shaping Mr. Trump’s second term.
Their dispute began days ago over the president’s signature domestic policy bill, which Mr. Musk had panned as a “disgusting abomination.” But it escalated uncontrollably on Thursday into a fight over who deserved more credit for Mr. Trump’s election victory, why Mr. Musk had not covered up his black eye with makeup during an Oval Office appearance last week and why Mr. Trump had abruptly dropped his support for a Musk associate nominated to lead NASA.
The sparring swiftly devolved into threats on their respective social media platforms, as Mr. Trump threatened to cut the billions in dollars in federal government contracts with Mr. Musk’s companies. For his part, Mr. Musk unleashed a tirade of attacks on the man he had once lavishly praised. He suggested it might be time to create a new political party, claimed there were references to Mr. Trump in government documents about the late financier and sex offender Jeffrey Epstein and indicated his support for a post calling for the president’s impeachment.