Elon Musk lost $79.4 billion on Thursday, the biggest single-day fall among the world’s billionaires, as Tesla and SpaceX shares slid on fears that the Democrats’ midterm sweep could bring fresh congressional scrutiny and tighter regulation to his companies.

Tesla shares fell 10.8% to their lowest level since August and SpaceX shares dropped 9% to around $123. Together the two declines pushed Musk’s fortune below $800 billion, less than a month after SpaceX’s initial public offering in June had carried him past $1 trillion. His wealth has dropped by about $90 billion over the past week, while he still remains the richest man in the world.

Musk still owns nearly 50% of SpaceX, though part of that stake is tied to performance-based vesting. Thursday’s loss ranks among his largest, after drops of $80 billion in August and $350 billion in June. Other technology billionaires were caught in the same sell-off: Michael Dell lost $22 billion, Jensen Huang $15.8 billion, Larry Ellison $10.8 billion and Mark Zuckerberg $8.4 billion.

The falls in Tesla and SpaceX tracked a wider tech sell-off. By the close on Thursday, the two companies had shed about $456 billion in market value since Tuesday’s close.

Musk had been the biggest donor to Republican candidates and causes in the midterms, with contributions topping $470 million, as the Financial Times first reported. Despite that spending, most of the candidates he backed lost. Democrats won control of both the House and the Senate. In Texas, where both Tesla and SpaceX are based, Democrats James Talarico and Gina Hinojosa beat longtime Musk allies, state Attorney General Ken Paxton and Governor Greg Abbott.

Deutsche Bank analysts wrote on Wednesday that while policy was hard to predict, they could envision SpaceX facing some incremental headwinds in that kind of backdrop. They noted that Hinojosa had made data centres a major campaign issue, calling for a moratorium on new approvals until the legislature passed stronger protections on water use, electricity costs, local control and incentives and criticising tax breaks for large facilities.

Both companies are building out artificial intelligence infrastructure in Texas, including Terafab, a planned facility in Grimes County that would combine a data centre with a sprawling semiconductor factory. SpaceX also plans a supercomputer at its Starbase launch site. Deutsche Bank analysts said SpaceX’s Texas compute capacity could now face delays and that capital expenditure might need to rise to meet tighter anticipated rules on data centre construction.

Musk and SpaceX have also been instructed to preserve records concerning restrictions imposed on a military version of the Starlink satellite internet service in Ukraine, restrictions that hampered the country’s ability to defend against Russian attacks.