S&P 500 futures were also 0.3% lower, and contracts tied to the tech-heavy Nasdaq dropped 0.5%. The three major indexes all tumbled on Tuesday, with the Dow shedding 400 points as investors worried the Iran conflict would escalate. President Donald Trump is willing to support groups in Iran who are willing to take up arms to overthrow the regime, The Wall Street Journal reported, citing U.S. officials.