The article refers to the class of situations in which abandoning the principle of legalism occurred in connection with the threat to the basic interests of a society and a state. The political history of the United States provides numerous examples of this kind of events. During international armed conflicts involving the US, civil wars or revolutions, the political leaders of this modern constitutional state have often decided to breach the law in order to overcome the danger threatening „the life of the nation”. One of the explanations for this state of affairs was the fact that the constitution of 1787, as distinguished from many other contemporary national constitutions, did not contain detailed solutions for the times of crisis. The activity of American presidents in the area of national security was grounded on expanding interpretations of their competences defined in the Basic Law. One of the theoretical grounds for president’s emergency power doctrine was the theory of prerogative elaborated by John Locke in the late 17th century. The article seeks to provide answer to the following paradox. Why did Locke, despite his involvement in developing the idea of the rule of law, also accept exercising extralegal prerogative powers in cases of emergency? The English philosopher defined the prerogative as „the power to act according to discretion, for the public good, without the prescription of the law, and sometimes even against it”. The idea of extralegal powers has become a recurring motif in the history of the United States’ liberal political culture. Proponents of this vision were convicted that uncertainty, contingency and an unforeseen cases are an inherent features of social and political life, which in many cases elude legal regulation. Recently, the renaissance of Locke’s theory of prerogative has taken place in connection with the war on terrorism, in form of an extralegal measures doctrine.