STORY: Wall Street ended lower on Tuesday, with the Dow dropping about a third of a percent, the S&P 500 shedding more than eight-tenths of a percent and the Nasdaq losing more than 1.4%.Investors worried about AI creating more competition for software makers, keeping them on edge ahead of quarterly results later this week from Alphabet and Amazon, shares of which both ended lower.Melissa Brown is managing director of investment decision research at SimCorp."Today, it seems that the AI trade in the U.S. is back to being questioned. I think things had gotten a little better for those stocks for a while. But we're seeing that, again, we've got stocks that have high valuations for sure. They have good earnings, but at some point their valuations get ahead of their future earnings, meaning they're expensive and are only going to get more expensive until we start to see a correction like this - so I think that maybe that trade is pausing for a bit."AI heavyweights Nvidia and Microsoft each fell almost 3%, while other tech names, including Salesforce and Adobe, lost around 7%, and Intuit slumped 11%.AI data firm Palantir bucked the trend, rallying almost 7% after strong quarterly results late on Monday.Healthcare stocks came under pressure after Wegovy maker Novo Nordisk warned that it expected a steep decline in annual sales. The company's U.S.-listed shares plummeted nearly 15%.Rival Eli Lilly shed about 4%, while obesity drugmaker Structure Therapeutics lost more than 6.5%.But it was a milestone day for Walmart, with shares climbing about 3%, making it the first brick-and-mortar retailer ever to hit $1 trillion in stock market value.