Stock Market Today: S&P 500, Dow Futures Rise, Nasdaq 100 Slips Ahead of Kevin Warsh's Jackson Hole Speech

U.S. stock futures show a mixed trend ahead of the market open, with the Dow slightly up while the Nasdaq remains down. Investors are focused on Federal Reserve Chairman Kevin Warsh's upcoming remarks at Jackson Hole and the impact of U.S. economic pressure on Iran. Individual stock movements are volatile, with significant swings for Marvell Technology, PayPal, and GAP.