For years, it paid off to buy stocks that were rising in price—and bet against struggling shares. The momentum trade was especially profitable this year, as investors piled into hot stocks including Micron Technology, Nvidia, Advanced Micro Devices and other artificial-intelligence darlings while wagering against those likely to be hurt by the embrace of AI.

The S&P 500 Momentum Index soared 44% in the second quarter, its best quarterly performance on record, and it surged 133% over the past five years, nearly double the broad market’s performance.

Mega funds and rookie investors alike piled into the trade, some using leverage and options contracts in an effort to amplify their returns, propelling the underlying shares higher.

“It is a self-fulfilling prophecy,” said Matthew Tym, managing director at Cantor Fitzgerald, of the trade.

Suddenly, the trade is a loser. The momentum index has tumbled more than 9% since July 1, lagging behind the S&P 500’s 2.8% gain. The index—which tracks stocks in the S&P 500 based on a “momentum score”—is on track for the biggest quarterly underperformance in 25 years. July was the second-worst month for the momentum trade in around 40 years, according to Bank of America estimates; the only month worse was April 2009, in the teeth of the global financial crisis.

Hedge funds that bought momentum shares while shorting low-momentum stocks suffered even more. At the same time, a basket of the most popular stocks held by hedge funds tracked by Goldman Sachs recorded its biggest one-month underperformance in July relative to the S&P 500 in more than 20 years, according to the bank’s analysts.

Momentum trading is based on a rather simple observation: Investments that go up tend to keep outperforming; those that underperform often remain laggards. This kind of trading might seem too simple a stock-picking strategy to work. Yet it often has.

“For decades, it didn’t take a lot of sophistication to run a momentum strategy and make a decent living at it,” says Agustin Lebron, senior researcher at EquiLibre, a trading firm.

Part of the reason: It takes a while for corporate and other information to spread to various investors, so they slowly build positions, producing buying momentum.

“A huge pension fund can’t flip around its positions in a day,” says Lebron. “Behavioral biases also account for some of the effect, as well—people tend to sell their winners too early and hold losers too long.”

Fans of the strategy point to the human tendency to extrapolate from past results—and chase investment returns—noting that momentum patterns have been evident in markets for decades, even centuries. They also say that some of the worst months for momentum strategies are during longer periods of outperformance.

Some have been doing the trade by buying the strongest investments in a sector while shorting the weakest; others lean in to rising markets or asset classes. Still others use a quantitative approach or turn to banks or others who sell ways to make distinct wagers on momentum as a “tradable factor” or a “thematic basket.”

The fans remain believers. “Any strategy has disappointing periods,” says Antti Ilmanen, global co-head of the portfolio solutions group at AQR Capital Management.

The surge in Moderna and other biotech stocks helped crush the momentum trade. These shares were among the most heavily shorted in recent years, but positive news on a cancer vaccine from Moderna and Merck sent those stocks flying, crushing some quant and other hedge funds. Moderna is up around 150% so far this month.

These traders had an especially rough day on Aug. 19, which Goldman Sachs told its clients was the worst day for “systematic long-short managers” in more than two years. About half of the losses were because of momentum trades, the bank said.

Some traders have begun to short, or bet against, the very stocks that propelled the momentum trade earlier this year. Net short positions in futures tied to the Nasdaq-100 index among speculators recently climbed to some of the highest levels of the past two decades, according to data from the Commodity Futures Trading Commission.

The about-face is a sign of how markets have become more treacherous for investors, even as indexes keep climbing. Part of the issue: the recent meltdown of Situational Awareness, a hedge fund that had piled into some of the most popular momentum shares, including chip stocks. After a period of market tumult, Nvidia shares rocketed almost 9% after its earnings, showing how quickly sentiment can shift.

Some investors say the run-up in share prices driving tech stocks higher reminds them at times of the dot-com frenzy decades ago.

Mike Ogborne, the founder of San Francisco-based Ogborne Capital Management, said he has grown more cautious on technology stocks and is keeping more of his portfolio in cash than he typically does.

And he is nervous about the surge in spending by technology giants and quarterly capital expenditures that keep rising.

“It is a little bit like Cinderella and the clock striking midnight. You don’t know when midnight is going to come around,” Ogborne said. “They don’t send a memo around telling you when the capex cycle is over.”

When Huang steps up to the mic for his company’s earnings call Wednesday, he will have the world’s attention. What he says about Nvidia’s present will preview the future of AI, dictate the path forward for a tech-crazed stock market and influence an American economy increasingly tethered to hopes that the boom won’t go bust.

The $5 trillion chip maker has provided the key building blocks for AI since the launch of ChatGPT in 2022 set off a race for dominance among OpenAI, Anthropic and established Silicon Valley giants. Now, as Nvidia backstops sprawling data-center projects and an exotic money pipeline to boost chip demand, the company’s influence is arguably bigger than ever.

But there are signs of trouble ahead. Political pushback to AI is growing. A bond selloff propelled borrowing costs to their highest levels in years. The hyperscalers that include some of Nvidia’s key customers—once cash-printing machines—are relying more on debt. OpenAI recently told investors its revenue rose by a tepid 18% in the second quarter while its losses deepened.

Nvidia is increasingly stepping in to shore up potential weak points across the market. Earlier this month, the company teamed up with six of Wall Street’s biggest firms on a $500 billion AI-financing plan, pledging to backstop lending to customers that can’t afford its chips otherwise. The chip maker last week also took a stake in Cloverleaf Infrastructure, which arranges power for data centers, and struck a $6 billion deal with startup Poolside aimed at developing a powerful open-weight AI model.

After watching shares in other chip makers and the so-called Magnificent Seven tech companies swing wildly in recent months, Wall Street is hoping Nvidia can beat expectations—again. The countdown is on.

“It’s kind of becoming more and more like the World Cup final than the Super Bowl at this point,” said Brian Mulberry, chief market strategist at Zacks Investment Management. “It’s just gotten to be that big.”

The company has smashed analysts’ earnings estimates for each of the 14 quarters since the AI boom kicked into high gear. Nvidia posted 210% annual growth in net income in its last three-month period, according to FactSet, making Wall Street’s 126% projection look pedestrian.

Expectations for a blowout second quarter have risen rapidly over the course of this year. All Nvidia will have to do to beat this target: outrun 95% annual earnings growth to more than $51.5 billion. Analysts project the chip maker will report record sales of $92 billion for the period, up from a forecast of $78 billion at the start of this year.

In July, big-tech earnings sparked volatility. Concerns about runaway capital spending spread across the sector after Alphabet’s and Tesla’s results, driving a $890 billion wipeout that contributed to the unwind of hedge fund Situational Awareness. Microsoft posted the largest one-day gain in market capitalization by any company, ever, after a quarter proving that it could still show investors the money. SpaceX rocketed higher after a record-breaking initial public offering, only to see $1 trillion in value evaporate.

Surging memory prices and borrowing costs have fueled fears that those and other companies will be unable to keep plowing more money into supplies including Nvidia chips. Shaia Hosseinzadeh, founder of OnyxPoint Global Management, has recently bought dips in AI-infrastructure stocks when Wall Street has strained to absorb massive debt issued by Silicon Valley.

“The macro data is really quite robust,” he said. “Of course, there’s a level at which everything breaks.”

Investors have kept pumping money into the AI trade despite concerns around chip consumers—and to the benefit of chip producers. That is why Nvidia’s outlook for semiconductor demand could send ripples through counterparts such as Micron Technology and Sandisk, developers of the data centers in which their chips reside, and a supply chain of power producers, contractors and other specialists that underpin the globe-spanning AI build-out.

“We joke internally that we’re all Nvidia analysts now,” said David Lefkowitz, head of U.S. equities at UBS Global Wealth Management.

The irony is that investors have tended to sell Nvidia stock immediately after blockbuster earnings, with shares falling each trading session after its four past quarterly reports. Some are betting that will be the case this time around, too.

The options market is pricing in a 5.3% swing, higher or lower, in Nvidia shares during the session following earnings, according to Option Research & Technology Services. That is higher than the 4.8% average move in Nvidia’s stock over the last 12 months after the company reports quarterly results.

In recent days, some of the most actively traded Nvidia options have been put contracts tied to the stock falling from its Friday value of $214.75 to $205 and $210 apiece, according to Cboe Global Markets data. Put options give the right to sell a stock by a set price and typically represent a bearish wager.

Many analysts remain optimistic. Frank Lee, global head of tech hardware and semiconductor research at HSBC Global Investment Research, recently raised his price target for Nvidia shares to $360 from $325, citing, among other things, Nvidia’s strategic partnerships with suppliers and its role as a top contributor to open-source AI.