The Dow Jones industrial average fell 1.7 percent, the broad S&P 500 index fell 1.0 percent, while the technology-heavy Nasdaq fell 1.1 percent.
On Friday, the US Supreme Court struck down Trump's tariffs. Over the weekend and on Monday, the president made a series of statements about global tariffs. There is now uncertainty in the market about what the tariff policy will be.
Several cybersecurity companies fell on concerns about how AI will affect their businesses. CrowdStrike, for example, fell about 10 percent.
Pharmaceutical company Eli Lilly rose 4.9 percent after announcing the launch of a new version of its weight-loss drug Zepbound. In addition, results from a study by Danish competitor Novo Nordisk were worse than expected.
