US stock markets experienced significant declines as tensions between the US and Iran escalated, prompting President Trump to reimpose a blockade in the Strait of Hormuz. The S&P 500, Dow, and Nasdaq all fell sharply, with semiconductor stocks leading the downturn as investors reacted to the geopolitical uncertainty. Oil prices surged in response to the new conflict, affecting market sentiment. Notably, futures pointed to a lower opening, indicating continued volatility in the markets as investors monitor developments in the Middle East and potential impacts on trade and global supply chains.