The U.S. stock market is tumbling toward one of its worst days since its springtime sell-off, as Nvidia and other AI superstar stocks keep dropping Thursday on worries their prices shot too high. Wall Street is also questioning whether the coming cuts to interest rates that it’s been banking on will actually happen.The S&P 500 sank 1.5% and pulled further from its all-time high set late last month. It’s on track for its worst day in a month and its second-worst since plunging in April after President Donald ...