In this case, David's enemy was a one time confidant, someone his equal that he had trusted in the affairs of the kingdom. This may not be the same type of enemy that we would have, does not have the same political effect, but, we feel the similarity just the same. The context must remain the extreme positions that these two men held and the severity of one man turning to injure the reputation of the other, the king. By the time David prays for a destruction, he is speaking in the plural.
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