http://writ.news.findlaw.com/dean/20020607.html"While our constitution contains no express provision for "emergency" or "crisis" situations, such a provision is not necessary. The U.S. Supreme Court made clear in Ex Parte Milligan, following the Civil War, that "the government, within the Constitution, has all the powers granted to it which are necessary to preserve its existence." Or as one commentator has added, "self-preservation is the first law of any nation."
Past presidents - principally Abraham Lincoln, Woodrow Wilson, and Franklin Roosevelt - by exercising their powers in time of emergency, have expanded their authority as necessary to meet emergencies they faced. They have, in essence, made the law in times of crisis, not always in the manner envisioned.
Lincoln launched the Civil War unilaterally, without Congressional action, following the secession of seven Southern states. Only later did he obtain Congressional approval. His critics called him a dictator. But he got the job done that had to be done.
Wilson asked for and received near dictatorial powers from Congress when attacks by Germany against American ships and submarines plunged the nation into World War I. He had to raise and equip a large army to fight on foreign soil. To do so, he demanded and received unprecedented new power and authority"
the autor says that it can be OK when the President is responsible and things go back to normal after the crisis.
He compares even with other democracies in similar situations.
the problem is : what happens if the President is not "normal" ?