U.S. President Donald Trump has taken a direct swipe at Elon Musk over the tech billionaire’s decision to float a new political movement, the America Party. In a strongly worded post on his Truth Social account Sunday night, Trump didn’t hold back, calling Musk’s move “ridiculous” and saying the Tesla CEO had gone “completely off the rails.”

“The one thing third parties are good for is creating complete and total disruption and chaos,” Trump wrote. “I am saddened to watch Elon Musk become a TRAIN WRECK over the past five weeks.”

The clash marks a sharp breakdown in what was once a close political alliance. Musk had been a major backer of Trump’s re-election efforts and was even tapped to head the Department of Government Efficiency (DOGE), created to cut federal spending.

But the relationship soured dramatically over disagreements on Trump’s latest tax and spending bill, which Musk publicly opposed. On Saturday, Musk finally pulled the trigger, announcing the creation of the America Party in a post on X (formerly Twitter), saying:

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

Trump, still fuming on Sunday, defended the traditional two-party structure and questioned Musk’s vision.

“We’ve had great success with the Republican Party. The Democrats have lost their way, but a third party? It’s just more confusion,” he said.

He also criticised Musk’s push for an Electric Vehicle (EV) mandate, revealing that his recently signed tax and spending law—which controversially cut food and healthcare programmes—intentionally ended tax breaks for EVs.