Regardless of the inability to declare war, the president does have the power to unilaterally order military action in defense of the United States pursuant to "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces". By U.S. law, this power is limited in that he must notify Congress within 48 hours after the beginning of military operations, explaining the source of his authority for the action. Once proper legal notification is given to the required members of Congress, military action can continue for up to 60 days without further authorization from Congress, or up to 90 days if the president "determines and certifies to the Congress in writing that unavoidable military necessity respecting the safety of United States Armed Forces requires the continued use of such armed forces in the course of bringing about a prompt removal of such forces."