A sell-off in technology stocks deepened on Friday as worries grew that Wall Street's frenzy around artificial intelligence had pushed prices too high. The S&P 500 tumbled 1.8% for its worst day since June, closing out a third straight losing week.

Technology weakness led the decline: the Nasdaq composite dropped a market-leading 2.9%, while the Dow Jones Industrial Average shed 572 points, or 1.1%.

Even after the tumble, the U.S. stock market remains just 3.1% below its all-time high — a level that has boosted the value of workers' 401(k) accounts — though the market has grown increasingly shaky with Tuesday's midterm elections in the United States approaching. Worries about AI in general have already become a concern for voters across political parties, and President Donald Trump has historically used the stock market's performance as a measure of his own success.

Intel led the way lower. The chipmaker's stock plunged 28.6%, its worst drop since 1974, after the company issued a profit forecast for the final three months of the year that fell short of analysts' expectations. CEO Lip-Bu Tan said the personal-computer industry continues to feel pressure. The plunge came even though Intel reported stronger profit for the latest quarter than analysts expected — a sign of how much more weight investors are currently placing on forward guidance than on past results.

Amazon fell 1.4% after reporting a weaker profit for the summer than analysts expected. Potentially more concerning for investors was the company's disclosure that it burned through $42.4 billion of cash over the prior 12 months, according to a measure called free cash flow — essentially the cash a company has left after funding its operations and big capital projects like AI data centers. Amazon spent $94.8 billion on property and equipment, primarily through investments in artificial-intelligence technology.

A day earlier, Alphabet's stock dropped more than 12% to its worst day on record, dragging the S&P 500 down with it, after the company told investors it burned through more cash during the summer than the spring. The parent of Google and YouTube cited similar, mammoth investments in AI.

Worries are rising about whether the hundreds of billions of dollars flowing into AI will produce enough profit and productivity to make the investment worthwhile, and the cash-burn disclosures from Amazon and Alphabet show how directly that question now lands on corporate balance sheets. At the same time, shares of computer chip companies and other winners from the race to build AI data centers have come under pressure on concerns that high interest rates may slow the further build-out of data centers.

"We're moving out of the hopes and dreams phase of the AI trade and into the 'show me' phase," said Joe Tigay, portfolio manager at Equity Armor Investments, in a note to investors. In other words, the burden of proof has shifted toward demonstrating returns on all that AI spending.

A drop of 4.2% for Nvidia, the chip company that became the poster child of the AI frenzy, was the heaviest force pulling the S&P 500 downward, outweighing even Intel. The gap comes down to index math: Nvidia's enormous market value gives each percentage point of its movement a larger effect on the S&P 500 than a far steeper fall in a smaller constituent such as Intel.

In the cryptocurrency industry, meanwhile, stocks tumbled following a hack on the world's biggest crypto exchange. The price of bitcoin fell below $77,000, down from more than $86,000 earlier this month, and a U.S.-based blockchain intelligence firm said a North Korean unit was likely behind the attack, which impacted more than $6 billion worth of crypto at Binance.

Coinbase Global fell 10.6% even though it reported stronger results for the latest quarter than analysts expected. Strategy, which says it owns about 4% of the total supply of bitcoin, fell 7.8%. It also reported a stronger profit for the latest quarter than analysts expected, while saying its chief financial officer will resign next week for personal reasons.

Outside of tech, stocks proved more resilient as many rallied after reporting stronger profits for the summer than analysts expected. Nearly as many stocks rose within the S&P 500 as fell.

ExxonMobil climbed 2.2%, and Chevron added 1.8% after the oil giants reported stronger profit for the summer than analysts expected.

Mondelez International rose 3.9% after the company behind Oreo cookies and Ritz crackers reported stronger-than-expected growth.

Colgate-Palmolive climbed 2.3% after higher prices for its products across much of the world helped it deliver better revenue and profit than analysts expected.

Expectations are high for U.S. companies' ability to make bigger profits, even though people around the world are feeling discouraged about high inflation and high fuel prices. Such expectations drove the S&P 500 to its record earlier this month, and with more quarterly reports due in the days ahead, they face a steady stream of tests.

All told, the S&P 500 fell 140.32 points to 7,580.07. The Dow Jones Industrial Average dropped 572.25 to 51,770.31, and the Nasdaq composite sank 747.73 to 25,437.00.

In the bond market, Treasury yields eased, a signal that investors were buying U.S. government bonds in search of something safer to own. The yield on the 10-year Treasury fell to 4.93% from 4.98% late Thursday and from more than 5.30% earlier in the month. Yields fell even though oil prices bounced higher, something that usually drives yields upward because it worsens inflation. The price for a barrel of Brent crude rose 2.4% to $113.43, near the high end of its range since the war with Iran sent oil prices and inflation higher.

In stock markets abroad, indexes were mixed in Europe following sharper swings in Asia. South Korea's Kospi dropped 3.5% as worries about AI hit its tech-heavy market, while the Hang Seng in Hong Kong climbed 1.5%. Japan's Nikkei 225 fell 2.1% after the Bank of Japan decided to keep interest rates steady, echoing moves made earlier in the week by the Federal Reserve and the European Central Bank.

AP Business Writers Yuri Kageyama and Michelle Chapman contributed to this report.

This story was originally featured on Fortune.com.