While the monarchy is the source of authority in Canada, in practice its position is mainly symbolic. The use of the executive powers is directed by the Cabinet, a committee of ministers of the Crown responsible to the elected House of Commons and chosen and headed by the prime minister (at present Justin Trudeau), the head of government. The governor general or monarch may, though, in certain crisis situations exercise their power without ministerial advice. To ensure the stability of government, the governor general will usually appoint as prime minister the individual who is the current leader of the political party that can obtain the confidence of a plurality in the House of Commons. The Prime Minister's Office (PMO) is thus one of the most powerful institutions in government, initiating most legislation for parliamentary approval and selecting for appointment by the Crown, besides the aforementioned, the governor general, lieutenant governors, senators, federal court judges, and heads of Crown corporations and government agencies. The leader of the party with the second-most seats usually becomes the leader of the Official Opposition and is part of an adversarial parliamentary system intended to keep the government in check.