Ackman and Icahn's feud escalates amidst Hindenburg report fallout.

Bill Ackman has reignited his feud with Carl Icahn by questioning the valuation of Icahn Enterprises (IEP), whose company has become the target of short-seller Hindenburg Research. Ackman said the situation had jeopardized Icahn’s fund and that the stock had dropped more than 50% since the Hindenburg report was published on May 2. Icahn has personally lost $15 billion. The bad blood between the moguls goes back two decades after a dispute over a 2003 deal involving Hallwood Realty.