U.S. stocks tumbled Monday after President Trump announced 15% temporary tariffs on imports, escalating trade policy uncertainty just days after the Supreme Court blocked his sweeping “reciprocal” tariffs. The S&P 500 fell 1%, the Dow Jones Industrial Average dropped 821 points or 1.7%, and the Nasdaq composite closed at 22,627.27, down 258 points.

The market’s unease reflects continued uncertainty over how U.S. trade policy will unfold. Despite the Supreme Court’s Friday ruling, Trump quickly moved to implement tariffs through alternative legal mechanisms, suggesting more clarity remains distant and trade tensions will persist.

Market Tumbles on Tariff Escalation

President Trump announced 15% temporary tariffs on imports Monday, reigniting trade policy uncertainty just three days after the Supreme Court blocked his sweeping “reciprocal” tariff regime. The S&P 500 fell 1%, the Dow Jones Industrial Average dropped 821 points or 1.7%, and the Nasdaq composite closed at 22,627.27, down 258 points.

The tariff announcement represents a step up from the 10% rate Trump announced Friday, which came immediately after the Supreme Court ruled that the president lacked legal authority for his broad tariff powers. Trump’s swift move to implement alternative tariff mechanisms signals that trade tensions will persist despite the court’s decision.

Chris Larkin, managing director of trading and investing at E-Trade from Morgan Stanley, said: “Stocks got a boost Friday from the Supreme Court’s tariff ruling, but it quickly became clear that the decision was simply going to open a new chapter in the trade saga, not end it.”

South Korea’s trade minister, Kim Jung-kwan, said Monday that uncertainty may worsen if the Trump administration continues imposing new tariffs under alternative laws. The prospect of prolonged trade friction kept investors cautious, though Monday’s losses remained modest compared to panic that swept global markets in April when Trump initially announced “Liberation Day” tariffs.

Tech Stocks Under Pressure From AI Competition

Investors continued punishing companies viewed as vulnerable to artificial intelligence competition. CrowdStrike fell 9.8%, extending its year-to-date loss to 25.3%. AppLovin sank 9.1%, bringing its decline for the year to 43.5%.

A tool from Anthropic that scans codebases for security vulnerabilities and suggests targeted software patches has been hitting stocks across the cybersecurity industry. Blue Owl Capital, which finances software companies facing competitive pressures, fell 3.4% to extend its year-to-date loss to 30.1%.

Nvidia is scheduled to report earnings Wednesday. Investors worry that technology giants including Alphabet and Amazon may be spending so heavily on Nvidia’s chips that they will not recover their investments through higher productivity and future profits.

Aviation and Pharmaceutical Moves

Airline stocks declined after heavy snow and high winds canceled thousands of flights across the Northeast. United Airlines lost 5.2%, American Airlines fell 4.9%, and Delta Air Lines sank 3.7%.

Novo Nordisk’s stock tumbled 16.4% after the Danish drugmaker said its CagriSema trial showed people lost a smaller percentage of weight after 84 weeks than with a competing drug from Eli Lilly. Eli Lilly rose 4.9%.

Bonds, Currencies, and the Fed

The 10-year Treasury yield fell to 4.03% from 4.08% late Friday. The U.S. dollar’s value edged lower against other currencies.

Bitcoin briefly fell below $64,000 but remained above the low point it reached earlier in the month. Gold continued to rise, benefiting from its reputation as a safer holding during times of economic uncertainty.

Fed Governor Christopher Waller said Monday that it is “a coin flip” whether the Federal Reserve will cut its main interest rate at its March meeting or stand pat. His comment represents a notable shift from January, when he was one of two Fed governors to dissent against the central bank’s decision to hold rates steady following three rate cuts at the end of last year.

Lower rates would provide economic stimulus that Trump has lobbied for aggressively. Rate cuts also carry the risk of worsening inflation.

International Markets

Stock indexes mostly fell in Europe following Friday’s Supreme Court ruling, which had boosted markets initially. In Asia, where markets got their first chance to react to the court’s decision, Hong Kong’s Hang Seng jumped 2.5%. South Korea’s Kospi rose a more modest 0.6%. Markets in Japan and mainland China were closed for holidays.