 Shares of CrowdStrike tumbled 11%. The Dow down 377 points. The Nasdaq lower by 144. S&P 500 down 40. American Express reported a 39% increase in profit from a year ago in its second quarter, while topping $2 billion in quarterly revenue from Cardi's. Amex also raised its full-year earnings guidance. However, that wasn't enough to impress investors, and its stock fell 3%.