Why is the stock market down today? [Video]

NEW YORK — Wall Street’s superstars tumbled Monday as a competitor from China threatens to upend the artificial-intelligence frenzy they’ve been feasting on.

The S&P 500 dropped 1.5%, dragged down in large part by a 16.9% fall for Nvidia. Other Big Tech stocks also took heavy losses, and they pulled the Nasdaq composite down 3.1% for its worst loss in more than a month.

The damage was focused on AI-related stocks, while the rest of the market held up much better. The Dow Jones Industrial Average rose 289 points, or 0.7%, and the majority of U.S. stocks climbed. But anyone holding an S&P 500 index fund, which are found in many 401(k) accounts, felt the pain because of how influential those tech giants have become on indexes.

The shock …