WASHINGTON (AP) - Former national security adviser Sandy Berger, the subject of a criminal investigation over the disappearance of terrorism documents, stepped aside on Tuesday as an informal adviser to Democratic presidential candidate John Kerry. "Mr. Berger does not want any issue surrounding the 9/11 commission to be used for partisan purposes. With that in mind he has decided to step aside as an informal adviser to the Kerry campaign until this matter is resolved," said Lanny Breuer, Berger's attorney. The investigation had threatened to become a political problem for Kerry a week before his nominating convention in Boston in...