Nvidia (NASDAQ: NVDA) stock is falling in Tuesday's trading. The artificial intelligence (AI) leader's share price was down 5.5% as of 2:45 p.m. ET amid a 0.9% decline for the S&P 500 index and a 1.6% pullback for the Nasdaq Composite index.

Chipmaker and AI darling Nvidia is back nipping at Apple's heels as the most valuable company in the world, with the stock hitting an all-time high Monday.

Investors are always scanning the horizon for the next big thing in stocks. For the past few years, it's clear that Nvidia (NASDAQ: NVDA) has been the key winner that's driven most index (and portfolio) returns.