What happens when the richest person and the most powerful politician have a knock-down, drag-out fight?

The world is finding out – and it's not a pretty picture. Donald Trump and Elon Musk have two of the biggest megaphones, and they have now turned them on each other, as a disagreement has ballooned into a war of words.

Trump has threatened Musk's voluminous business dealings with the federal government, which form the lifeblood of his SpaceX programme.

"The easiest way to save money in our budget, billions and billions of dollars, is to terminate Elon's governmental subsidies and contracts," Trump posted menacingly on his own social media website.

If Trump turns the machinery of government against Musk, the tech billionaire will feel pain. Tesla's stock price plunged by 14% on Thursday.

It's not a one-way street, however. After that volley, Musk called for Trump's impeachment, dared him to cut funding for his companies and countered that he was accelerating the decommissioning of his Dragon spacecraft, which the US relies on to carry American astronauts and supplies to the International Space Station.

Musk has near limitless resources to respond, including by funding insurgent challengers to Republicans in next year's elections and primaries. And late on Thursday afternoon, he said he was dropping the "really big bomb" – suggesting without evidence that Trump appears in unreleased files related to late sex offender Jeffrey Epstein.

His press secretary, Karoline Leavitt, offered only a tepid pushback to Musk's allegations and accusations.

"This is an unfortunate episode from Elon, who is unhappy with the One Big Beautiful Bill because it does not include the policies he wanted," she said.

Musk may not win a fight against the whole of Trump's government, but he could exact a high political - and personal - price for Trump and the Republicans.

Trump, perhaps aware of this, appeared to tamp down the heat a bit by the end of the day, avoiding comment on Musk during a public appearance at a White House police appreciation event and posting a message on Truth Social that said he didn't mind "turning against him" but wishes he had quit government service months ago. He then pivoted to boosting of his "big, beautiful" tax and spending legislation.

It's difficult to envision an easy walk-down after Thursday's heat, however.

The feud started at a simmer last week, began bubbling on Wednesday and became a full-on boil on Thursday afternoon in the Oval Office. As new German Chancellor Friedrich Merz – the day's visitor – sat in awkward silence, the president sounded a bit like a spurned lover.

He expressed surprise at Musk's criticism of his legislation. He pushed back against the notion that he would have lost last year's presidential election without Musk's hundreds of millions of dollars in support. And he said Musk was only changing his tune now because his car company, Tesla, will be hurt by the Republican push to end electric vehicle tax credits.

Musk quickly took to his social media site, X, with a very Generation X response for his 220 million followers: "Whatever". He said he didn't care about the car subsidies, he wanted to shrink the national debt, which he says is an existential threat to the nation. He insisted that Democrats would have prevailed in last year's election without his help. "Such ingratitude," he told Trump.

The billionaire then launched a series of extraordinary attacks throughout the afternoon, and the feud was on in earnest.

Musk and Trump had formed a powerful but unlikely alliance, culminating in the tech billionaire having a key position of budget-slashing authority in the Trump administration. Musk's Department of Government Efficiency, or Doge, became one of the biggest stories of Trump's first 100 days, as it shuttered entire agencies and dismissed thousands of government workers.

It wasn't long, however, before speculation began over when – and how - the two outsized personalities would ultimately fall out.

For a while, it seemed like those predictions were off the mark. Trump stood by Musk even as the latter's popularity dropped, as he feuded with administration officials and as he became a liability in several key elections earlier this year.

Every time it appeared there would be a break, Musk would pop up in the Oval Office, or the Cabinet room or on the president's Air Force One flight to Mar-a-Lago.

When Musk's 130 days as a "special government employee" ended last week, the two had a chummy Oval Office send-off, with a golden key to the White House and hints that Musk might someday return.

It's safe to say that any invitation has been rescinded and the locks have been changed.

"Elon and I had a great relationship," Trump said on Thursday – a comment notable for its use of the past tense.

There had been some thought that Trump's surprise announcement on Wednesday night of a new travel ban, additional sanctions on Harvard and a conspiracy-laced administration investigation of former President Joe Biden were all efforts to change the subject from Musk's criticism. The White House and its allies in Congress seemed careful not to further antagonise him after his earlier comments.

Then Trump spoke out and… so much for that.

Now the question is where the dispute goes next. Congressional Republicans could find it harder to keep their members behind Trump's bill with Musk providing rhetorical and, perhaps financial, air cover for those who break ranks.

Trump has already threatened Musk's government contracts, but he could also take aim Musk's remaining Doge allies in the administration or reopen Biden-era investigations into Musk's business dealings.

Everything at this point is on the table.

Meanwhile, Democrats are on the sidelines, wondering how to respond. Few seem willing to welcome Musk, a former donor to their party, back into the fold. But there's also the old adage that the enemy of an enemy is a friend.

"It's a zero-sum game," Liam Kerr, a Democratic strategist, told Politico. "Anything that he does that moves more toward Democrats hurts Republicans."

At the very least, Democrats seem happy to stand back and let the two men exchange blows. And until they abandon this fight, the din is likely to drown out everything else in American politics.

But don't expect this spat to end anytime soon.

"Trump has 3.5 years left as president," Musk wrote on X, "but I will be around for 40-plus years."