The market sell-off intensified on Monday, with the S&P 500 and Nasdaq falling below their 50-day moving averages for the first time in 138 trading days. The Dow Jones Industrial Average experienced its worst three-day decline since April, as investors offloaded assets including gold, cryptocurrencies, and high-flying tech stocks. This downturn comes as markets brace for a critical test of whether the AI-driven rally and economic growth that propelled record stock gains in 2025 can sustain into the new year.