Jim Cramer urged investors to stop using borrowed money for artificial intelligence stocks as U.S. margin debt climbed above $1.5 trillion. Jim Cramer thinks investors who are borrowing to pursue those returns are taking an unacceptable risk. The Financial Industry Regulatory Authority said debit balances in customer securities margin accounts hit $1.502 trillion in June. The surge doesn't mean all the borrowed money went into AI stocks. Rising margin debt sharpens Cramer's AI warningBuying on margin allows investors to buy more stock than they could if they just used cash.