Nvidia Corp. shares are down 9.1% since hitting a record on Oct. 29, well underperforming the S&P 500 Index, as investors grow concerned about the sustainability of artificial intelligence spending and the chip giant’s grip on the market. The recent drop is notable considering that on the day the stock last closed at an all-time high, it was up more than 1,300% since the end of 2022 and Nvidia’s market capitalization was over $5 trillion compared with roughly $400 billion less than three years earlier. Meanwhile, the dominant AI chipmaker is facing more competition than ever before from rivals like Advanced Micro Devices Inc., as well as its biggest clients, including Alphabet Inc. and Amazon.com Inc. And Wall Street is growing increasingly worried about Nvidia’s investments in many of its customers, which could be seen as artificially propping up demand.