U.S. President Donald Trump lashed out against Elon Musk after he formed a new political party, calling the move “ridiculous,” and saying the tech billionaire had gone “completely off the rails.”

“I am saddened to watch Elon Musk go completely ‘off the rails,’ essentially becoming a TRAIN WRECK over the past five weeks,” Trump said in a post on Truth Social late Sunday stateside. “The one thing Third Parties are good for is the creation of complete and total disruption and chaos.”

Musk said in a post on X Saturday that he had set up the “American Party” to compete against the Republican and Democratic parties. The billionaire had teased for weeks the idea of a new political party, taking on Trump over the tax and spending plans that he said would bankrupt the economy.

“By a factor of 2 to 1, you want a new political party and you shall have it!” Musk wrote, “Today, the America Party is formed to give you back your freedom.”

Disagreement over the spending bill had led to a dramatic falling out between Trump and Musk, souring the bromance which saw Musk spend millions of dollars sponsoring Trump’s re-election bid and the president appoint Musk to lead the Department of Government Efficiency, known as DOGE, tasked with identifying areas to cut federal spending.

“I think it’s ridiculous to start a third party. We have a tremendous success with the Republican Party. The Democrats have lost their way, but it’s always been a two-party system, and I think starting a third party just adds to confusion,” Trump said Sunday, Reuters reported, a day after Musk’s announcement.

Trump also took aim at Musk’s push for an “Electric Vehicle Mandate” in the Sunday post, saying it would have “forced everyone to buy an Electric Car in a short period of time.”

The president’s tax and spending cut bill, which was signed into law on July 4, put an end to tax credits for buyers of electric vehicles.

Trump said in the post that he had warned Musk during his presidential campaign that he planned to terminate the EV tax credit if he won a second term.

“When Elon gave me his total and unquestioned Endorsement, I asked him whether or not he knew that I was going to terminate the EV Mandate – It was in every speech I made, and in every conversation I had. He said he had no problems with that,” Trump said.

Musk’s announcement drew criticism from Trump’s allies such as James Fishback, CEO of investment firm Invest Azoria.

Fishback said he postponed an initial public listing of its Azoria Tesla Convexity ETF, “in direct response” to Musk’s formation of a new party, and urged the Tesla’s board to rein him in.

“This creates a conflict with his full-time responsibilities as CEO of Tesla. It diverts his focus and energy away from Tesla’s employees and shareholders,” Fishback said in a post on X.