• Musk forms 'America Party' opposing Trump's tax bill

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• Musk criticizes Trump's tax bill as harmful to U.S. economy

• Musk plans to unseat lawmakers supporting Trump's tax bill

The tattered bromance between Republican President Donald Trump and his main campaign financier Elon Musk took another fractious turn on Saturday when the space and automotive billionaire announced the formation of a new political party, saying Trump's "big, beautiful" tax bill would bankrupt America.

A day after asking his followers on his X platform whether a new U.S. political party should be created, Musk declared in a post on Saturday that "Today, the America Party is formed to give you back your freedom."

"By a factor of 2 to 1, you want a new political party and you shall have it!" he wrote.

The announcement from Musk comes after Trump signed his self-styled "big, beautiful" tax-cut and spending bill into law on Friday, which Musk fiercely opposed.

Musk, who became the word's richest man thanks to his Tesla car company and his SpaceX satellite firm, spent hundreds of millions on Trump's re-election and led the Department of Government Efficiency from the start of the president's second term aimed at slashing government spending.

The two have since fallen out spectacularly over disagreements about the bill.

Musk said previously that he would start a new political party and spend money to unseat lawmakers who supported the bill.

Trump earlier this week threatened to cut off the billions of dollars in subsidies that Musk's companies receive from the federal government.

Republicans have expressed concern that Musk's on-again, off-again feud with Trump could hurt their chances to protect their majority in the 2026 midterm congressional elections.

Asked on X what was the one thing that made him go from loving Trump to attacking him, Musk said: "Increasing the deficit from an already insane $2T under Biden to $2.5T. This will bankrupt the country."

He referenced the growth of Greece from subjugation to preeminence in the ancient world in another tweet, saying: "The way we're going to crack the uniparty system is by using a variant of how Epaminondas shattered the myth of Spartan invincibility at Leuctra: Extremely concentrated force at a precise location on the battlefield."

There was no immediate comment from Trump or the White House on Musk's announcement.

The feud with Trump, often described as one between the world's richest man and the world's most powerful, has led to several precipitous falls in Tesla's share price.

The stock soared after Trump's November reelection and hit a high of more than $488 in December, before losing more than half of its value in April and closing last week out at $315.35.

Despite Musk's deep pockets, breaking the Republican-Democratic duopoly will be a tall order, given that it has dominated American political life for more than 160 years, while Trump's approval ratings in polls in his second term have generally held firm above 40 percent, despite often divisive policies.