The S&P 500 took a pause from its recent gains on Tuesday as doubts about the sustainability of the artificial intelligence bull trend worried investors.

The broad market index closed down 0.6% after reaching a new all-time intraday high earlier in the session and posting a record close on Monday. The Nasdaq Composite fell 1%, with the losses led by AI names like Nvidia, Oracle and Amazon. The Dow Jones Industrial Average was 60 points, or 0.1%, lower.

Nvidia shares were down 2% a day after the chipmaker announced a $100 billion investment in OpenAI, which boosted its stock and the whole equity market. Some investors were rethinking the deal between customer and supplier for its resemblance to events seen in the dot-com bubble. Investors also raised questions about whether there is enough energy to power the growth plans by the two marquee AI companies.

Oracle, which is up more than 50% in three months because of an optimistic AI sales forecast, was off by 4%.

“While the initial reaction to Nvidia’s investment in OpenAI was positive, investors quickly realized that Nvidia may be OpenAI’s only option to get the capital it needs right now, an investor of last resort,” said Gil Luria, head of technology research at D.A. Davidson. “OpenAI has overextended itself by making commitments well beyond its means, and Nvidia may have been the only equity investor willing to help.”

Federal Reserve Chair Jerome Powell furthered valuation concerns Tuesday, noting “equity prices are fairly highly valued.” Powell also signaled that the rate-cutting path wasn’t clear and that it was a “challenging situation.”

Still, the broader market kept losses to a minimum. The small-cap Russell 2000 managed to reach an all-time high during the session and remained in the green, riding enthusiasm about a Fed rate cut last week.

Investors are awaiting Friday’s release of the latest reading of the personal consumption expenditures price index, which is the Fed’s preferred inflation measure.

Traders were also watching an increasing chance of a government shutdown ahead of a Sept. 30 deadline after the Senate last week rejected Republican and Democratic proposals to at least temporarily fund the federal government. On Tuesday, Trump canceled a planned meeting this week with top Democrats in Congress, saying that no meeting “could possibly be productive.”