Shares of Elon Musk's electric vehicle maker are falling sharply Thursday as investors fear his dispute with President Donald Trump could end up hurting the company.

Tesla plunged more than 10% in the afternoon as a disagreement over the U.S. president's budget bill turned nasty. After Musk said that Trump wouldn't haven't gotten elected without his help, Trump implied that he may turn the federal government against his company.

"The easiest way to save money in our Budget, Billions and Billions of Dollars, is to terminate Elon's Governmental Subsidies and Contracts," Trump wrote on his social messaging service Truth Social. "I was always surprised that Biden didn't do it!"

The drop on Thursday wiped out more than $100 billion from Tesla's market value, partially reversing a big runup in the eight weeks since Musk confirmed that Tesla would testing an autonomous, driverless "robotaxi" service in Austin, Texas, this month.

Investors fear Trump might not be in such a rush to usher in a future of self-driving cars in the U.S., and that could slam Tesla because so much of its future business depends on that.

"There is a fear that Trump is not going to play Mr. Nice Guy when in come to autonomous," said Wedbush Securities analyst Dan Ives. "The whole goal of robotaxis is to have them 20 or 25 cities next year. If you start to heighten the regulatory environment, that could delay that path." Tesla shares doubled in the weeks after Trump was elected, hitting an all-time high on Dec. 17. They gave back those gains and more during Musk's time as head of a government cost-cutting group.

In April, Musk vowed to focus much more on Tesla and its upcoming launch of driverless taxis, pushing up the value of the company on the market by more than $400 billion.