The President of the United States has available certain powers that may be exercised in the event that the nation is threatened by crisis, exigency, or emergency circumstances (other than natural disasters, war, or near-war situations). Such powers may be stated explicitly or implied by the Constitution, assumed by the Chief Executive to be permissible constitutionally, or inferred from or specified by statute. Through legislation, Congress has made a great many delegations of authority in this regard over the past 200 years.