"They are truly cowards in the worst way," says filmmaker Robert Greenwald, of the notorious billionaires Charles and David Koch. And he should know. After he released his 2012 documentary, "The Koch Brothers Exposed," Koch-funded organizations took out ads trying to discredit Greenwald and his work, yet the brothers still declined his repeated offers to debate the topics covered in the film, like the re-segregation of schools and the defanging of the EPA. "I wanted to engage in a policy debate," he says. "But they won't engage."