U.S. stock markets experienced a significant decline as the Dow dropped approximately 350 points following a record-breaking run last week. Investors are wary ahead of Nvidia earnings and a speech from Fed Chief Powell, which have created a cautious atmosphere. The S&P 500 and Nasdaq also fell, with traders reacting to fading rate-cut optimism and inflation concerns. Wall Street ended lower, emphasizing the uncertainty in the market as stocks waver and direction remains unclear.