What just happened? At 9:45 AM ET, the S&P 500 was trading nearly +1.5% higher and tech stocks were sharply higher. At 10:40 AM ET, selling pressure began to intensify without any major headlines in one of the biggest reversals of the year. Just 2 hours later, President Trump said Iran shot down a US helicopter "last night" and that the US must "respond to this attack." This sent the S&P 500 to a new low of the day, down 240 points since 9:45 AM ET. In just 3 hours, the S&P 500 has erased -$2.1 trillion in market cap. Volatility is back.