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Since the United States embarked on its "war on drugs" in the l980s, law enforcement officers have routinely been allowed to testify as expert and non-expert witnesses as to their opinions on how drug dealers operate and how to translate drug jargon. From the government's perspective, this practice makes perfect sense. Opinion testimony by police and federal agents aligned with the prosecution can ensure that jurors draw inculpatory conclusions from a defendant's ambiguous behavior and communications. Faced with a choice, a prosecutor will always prefer the cop to cooperating witnesses, who probably participated in the underlying crime, cut a deal, and have their own criminal history. Even when cooperating witnesses appear credible, they will only be allowed to testify to events that they personally witnessed. Police officers have none of this baggage, and their opinions can exert a powerful influence on the jury.