An US cable with an assement in it proves the existence of the assesments, not that the assesment is right. Example: an US cable pretends that Iran has Korean missiles. Such an cable proves only that US thinks that Iran have them. It get not the status of evidence of the fact of possession by Iran by leaking the assesment. So anybody can prove his assesment by leaking it I dont say that Iran has no Korean missiles, but only that an leaked us cable has no evidential value. Maybe revealed facts in the cable, but not the assesment itself. Idem the assesment of Netanyahu dont prove that he never kept his promises but only that US experienced Netanyahu as an liar, probably right but it is no evidence he is.
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from the article: Netanyahu: WikiLeaks cables prove Israel is right on Iran