WASHINGTON (Reuters) -President Donald Trump on Sunday called Elon Musk's plans to form a new political party "ridiculous," launching new barbs at the tech billionaire and saying the Musk ally he once named to lead NASA would have presented a conflict of interest given Musk's business interests in space.

A day after Musk escalated his feud with Trump and announced the formation of a new U.S. political party, the Republican president was asked about it before boarding Air Force One in Morristown, New Jersey, as he returned to Washington upon visiting his nearby golf club.

"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 told reporters.

"It really seems to have been developed for two parties. Third parties have never worked, so he can have fun with it, but I think it's ridiculous."

Shortly after speaking about Musk, Trump posted further comments on his Truth Social platform, saying, "I am saddened to watch Elon Musk go completely 'off the rails,' essentially becoming a TRAIN WRECK over the past five weeks."

Musk announced on Saturday that he is establishing the "America Party" in response to Trump's tax-cut and spending bill, which Musk said would bankrupt the country.

"What the heck was the point of @DOGE if he's just going to increase the debt by $5 trillion??" Musk wrote on X on Sunday, referring to the government downsizing agency he briefly led. Critics have said the bill will damage the U.S. economy by significantly adding to the federal budget deficit.

Musk said his new party would in next year's midterm elections look to unseat Republican lawmakers in Congress who backed the sweeping measure known as the "big, beautiful bill."

Musk spent millions of dollars underwriting Trump's 2024 re-election effort and, for a time, regularly showed up at the president's side in the White House Oval Office and elsewhere. Their disagreement over the spending bill led to a falling out that Musk briefly tried unsuccessfully to repair. 

Trump has said Musk is unhappy because the measure, which Trump signed into law on Friday, takes away green-energy credits for Tesla's electric vehicles. The president has threatened to pull billions of dollars Tesla and SpaceX receive in government contracts and subsidies in response to Musk's criticism.

NASA APPOINTMENT 'INAPPROPRIATE'

Trump in his social media comments also said it was "inappropriate" to have named Musk ally Jared Isaacman as NASA administrator considering Musk's business with the space agency. In December Trump named Isaacman, a billionaire private astronaut, to lead NASA but withdrew the nomination on May 31, before his Senate confirmation vote and without explanation.

Trump, who has yet to announce a new NASA nominee, on Sunday confirmed media reports he disapproved of Isaacman's previous support for Democratic politicians.

"I also thought it inappropriate that a very close friend of Elon, who was in the Space Business, run NASA, when NASA is such a big part of Elon's corporate life," Trump said on Truth Social. "My Number One charge is to protect the American Public!"

Musk's announcement of a new party immediately brought a rebuke from Azoria Partners, which said on Saturday it will postpone the listing of its Azoria Tesla Convexity exchange-traded fund because the party's creation posed "a conflict with his full-time responsibilities as CEO." Azoria was set to launch the Tesla ETF this week. 

Azoria CEO James Fishback posted on X several critical comments about the new party and reiterated his support for Trump. 

"I encourage the Board to meet immediately and ask Elon to clarify his political ambitions and evaluate whether they are compatible with his full-time obligations to Tesla as CEO," Fishback said.