"I do ask every publisher, every editor, and every newsman in the nation to reexamine his own standards, and to recognize the nature of our country's peril. In time of war, the government and the press have customarily joined in an effort based largely on self-discipline, to prevent unauthorized disclosures to the enemy. In time of "clear and present danger," the courts have held that even the privileged rights of the First Amendment must yield to the public's need for national security."