Wall Street traders are ill-prepared for an expected sharp 10% plunge in the S&P 500 triggered by the escalating war in Iran , JPMorgan Chase & Co.’s trading desk warned Monday, as oil prices soared past $100 a barrel and risks of economic stagnation loomed. Andrew Tyler, head of global market intelligence at the financial giant, shifted to a “tactically bearish” stance on US stocks as the conflict entered its second week, with no end in sight. Such a correction from the index’s peak would drag