Cracks in the relationship between President Trump and Tesla CEO Elon Musk, his self-proclaimed “First Buddy,” are scaring Tesla shareholders as the two fired salvos at each other in increasingly heated rhetoric on Thursday.

Shares dropped on Thursday as Musk publicly criticised the tax bill the US president is pushing to enact into law.

Tesla shares dropped more than 5% on Thursday on a day otherwise devoid of news for the electric vehicle maker, leading traders to speculate that Musk's increasingly pointed rhetoric suggests strain in the relationship that has benefited his sprawling empire of businesses.