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- Jeremy Grantham warned US stocks and the economy are headed for trouble.
- The elite investor and market historian said the AI frenzy is a bubble that's bound to burst.
- Grantham predicted a decade of disappointment for stocks and flagged several long-term threats.
Jeremy Grantham says US stocks are massively overvalued and poised to tumble, the AI craze is a bubble that will pop, and the defiant American economy is headed for trouble.
The S&P 500 has surged 30% to record highs since the start of last year, but there has "never been a sustained bull market" with a backdrop like today's, Grantham told the Exchange conference in Miami this week.