This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong; it cannot perjure itself; it cannot be wholly absent. Only its interpretation can err.
Oath definition, a solemn appeal to a deity, or to some revered person or thing, to witness one's determination to speak the truth, to keep a promise, etc.: to testify upon oath. See more. Dictionary.com
The oath of office of the President of the United States is the oath or affirmation that the President of the United States takes after assuming the presidency but before he or she begins the execution of the office. The wording of the oath is specified in Article II, Section One, Clause 8 of the United States Constitution.