Jeremy Grantham, the co-founder and long-term investment strategist at GMO Asset Management, returned to CNBC Squawk Box with one of the bleakest market calls of his career. Grantham, who says GMO manages roughly $85 billion, called this “the most expensive market in American history” and warned that a reversion to trend would be closer to ... Jeremy Grantham Warns U.S. Stocks Could Plunge 70% in the Most Expensive Market in History