Tesla CEO and former adviser to Donald Trump, Elon Musk, hit back at the US president on Thursday after Trump said he was “disappointed” by the billionaire’s public opposition to the sweeping tax-cut and spending bill.

Taking to his X social media platform as Trump was still speaking, Musk published a string of posts, denying Trump’s statement that Musk “knew the inner workings” of the bill better than anyone in the Oval Office.

Shares of electric vehicle maker Tesla were down 9% following the outbursts, to their lowest level since late February.

The back-and-forth made it clear tensions had reached a boiling point between the world’s most powerful man and the world’s richest man, after weeks of speculation that they were headed for a clash of egos.

Musk, whose other companies include rocket company and government contractor SpaceX and its satellite unit Starlink, spent nearly $300 million in the 2024 election in support of Trump and other Republican candidates.

Starting on Tuesday, the tech executive unleashed a series of blistering attacks against what Trump calls his “big, beautiful bill.”

Musk called it a “disgusting abomination” that would deepen the federal deficit, amplifying a rift within the Republican Party that could threaten the bill’s prospects in the Senate.

In retaliation, Trump suggested that he may terminate US government contracts and subsidies given to Musk’s companies.

“The easiest way to save money in our Budget, Billions and Billions of Dollars, is to terminate Elon’s Governmental Subsidies and Contracts,” Trump said in a Truth Social post.