Leopold Aschenbrenner’s hedge-fund firm Situational Awareness is down around 67% so far in July after incurring heavy losses on AI stocks, according to a person who saw a letter the firm sent to investors Thursday. “We let you down this month,” Aschenbrenner wrote in the investor letter, the contents of which were described to The Wall Street Journal. The deep losses prompted the firm to sell the bulk of its stockholdings to Ken Griffin’s investment firm Citadel as it raced to gather cash to cover margin calls from its lenders. Situational went so far as to reach a deal late…