US stocks retreated on Monday as shares of AI darling Nvidia (NVDA) tanked and a looming deadline fueled economic uncertainty around President Donald Trump’s tariff plans. The S&P 500 (^GSPC) fell 1% while the tech-heavy Nasdaq Composite (^IXIC) dropped 1.5%. The Dow Jones Industrial Average (^DJI) fell 0.6%, as the major US indexes came off a volatile week and a losing February. Nvidia stock plummeted as much as 7% on Monday as reports surfaced that the tech giant’s AI chips are reaching China despite export controls. March trading kicked off with investors encountering more questions than answers as tariff deadlines…