The Constitution, is silent as to Emergency Powers of the President. However, Presidents, since President Washington have taken powers that are not explicitly defined by the Constitution. The Congress passed Presidential Emergencies Act in 1976.
.Background on Emergency Powers of the President — by Marc Schulman
Presidents have traditionally taken broad powers in an emergency, powers that the constitution has not explicitly accorded them. Presidential scholar Richard Pius called these "Prerogative Powers", i.e., powers not necessarily given to a President by the Constitution, but which the President has taken. Pius quoted Theodore Roosevelt at the end of his Presidency when he wrote:
"While President I have been President, emphatically. I have used every ounce of power there was in the office and I have not cared a rap for the criticisms of those who spoke of my 'usurpation of power': for I know that the talk has been all nonsense and that there had been no usurpation .. in showing the strength of, or giving strength to, the executive, I was establishing a precedent of value.”
One of the successes of the Constitution has been a certain ambiguity as to the meaning of some of its clauses. That has allowed the Constitution to be interpreted differently over time. Article II confers the “Executive Power shall be vested in President.” What are the limits of those powers? The President is responsible for “faithfully executing the law.” However, to which' law' does this refer? The President is the Commander-in-Chief, but how much power do Excecutive Powers give the President?
From the earliest time, questions have been raised to assess the limits of Presidential power. President Washington issued a Proclamation of Neutrality, which many challenged his right to grant. James Madison, the prime author of the Constitution, believed that the Proclamation of Neutrality went too far. However, Madison did not have the votes in the Congress to override Washington’s actions. As a result, Washington created a precedent.
One Hundred Fifty years later, President Franklin D. Roosevelt took the same position as Washington regarding the powers of the presidency. While Congress wanted to keep the US neutral in the initial years of World War II, Roosevelt was committed to helping the Allies, as much as he could. When Great Britain ran out of funds, FDR unilaterally announced Lend-Lease. Roosevelt also entered into an agreement with Great Britain where he gave them destroyers, in return for bases. This was a blatant exercise of power that the President did not have, however, he consulted with Congress and obtained their silent approval for going forward. Later on, Congress authorized money to renovate the bases, thus giving its consent, after the fact, .
That all the acts, proclamations, and orders of the President of the Untied States after the fourth day of March (day Lincoln was inagurated) eighteen hundred and sixty-one, respecting the army and navy of the United States, and calling out or relating to the militia or volunteers from the States, are nearby approved and in all respects legalized and made valid, to the same effect as if they had been issued and done, under the previous express authority and direction of the Congress of the United States.
Sometimes the President goes too far. An example of Presidential over-reach was the attempt by President Truman to seize the steel mills during the Korean War. However, the Supreme Court ruled that doing so would exceed Truman's authority.
The President's ability to engage in war was limited by the War Powers Act. The act limited the ability of the President to announce a National Emergency.
In September 1976, the Presidential Emergencies Act was passed. The Act allowed the President to declare an Emergency, however, required the President to notify Congress of the nature of the Emergency. An Emergency, as declared by the President, automatically ended after one year if not renewed.
When the Presidential Emergencies Act was initially passed, it was thought that the emergency declared by the President could be terminated by joint resolution of Congress. Since that time, it has been understood that such a joint resolution would be subject to a Presidential veto, and thus, Congress would require a 2/3 majority to override a veto.
Presidents have declared an Emergency 31 times since the Act was passed. Here is a list. All of these listed emergencies have been related to foreign affairs.