Musk had previously stated that he would form a new political party and spend money to overthrow lawmakers who support the bill.
Trump threatened earlier this week to cut billions in subsidies that Musk's companies receive from the federal government.
Republicans have expressed concern that Musk's ongoing feud with Trump could jeopardize their chances of maintaining a majority in the 2026 midterm elections.
When asked on X what made him shift from loving Trump to attacking him, Musk said: "Increasing the deficit from $2 trillion, which was already insane under Biden, to $2.5 trillion. This will bankrupt the country."
There has been no immediate comment from Trump or the White House regarding Musk's announcement.
The feud with Trump, often described as a rivalry between the richest man in the world and the most powerful man in the world, has led to significant declines in Tesla's stock price.
Shares surged after Trump was re-elected in November, reaching over $488 in December, before losing more than half of their value by April and closing last week at $315.35.
Despite Musk's deep pockets, breaking the monopoly between the Republican-Democrat parties will be a tall order, as it has dominated American political life for over 160 years, while Trump's approval ratings in polls during his second term generally hover above 40%, despite policies that often divide.