United States markets dropped on Thursday as artificial intelligence and chip shares led a broad selloff, reversing Wednesday's relief rally that followed the Democratic midterm sweep.

By midday the tech heavy Nasdaq was down about 4.8 percent, the S&P 500 about 3.6 percent and the Dow about 2.8 percent. Investors who had first welcomed limits on unilateral White House policy shocks pivoted to a different fear: that newly empowered Democrats in Congress and in the states will slow data centre building and tighten oversight of an AI industry that has driven much of the recent bull run.

That reading matches commentary from market desks and from executives who already admit the sector fuelled public hostility with its land, power and water demands. Shares linked to SpaceX and other high flying tech names were also caught in the downdraft as traders cut risk across speculative growth stories.

Politics and portfolios are now tightly braided. Democrats campaigned in part on anger at Silicon Valley influence and at the costs of the AI buildout, while heavy campaign spending by technology billionaires failed to stop the blue wave in several races. Markets that once treated AI capacity as a one way bet are repricing political permission as a scarce input.

None of this proves regulation will arrive at the speed traders fear. It does show that after the midterms, the assumption of frictionless expansion for data centres and model trainers is no longer the default on Wall Street.