Schlesinger, Arthur M. The Imperial Presidency. Boston: Houghton Mifflin, 2004.
The Constitution granted the President extraordinary power and authority in leading America in foreign affairs. As a consequence, the modern President has been able to expand his powers to enormous levels out of times of foreign crises. The Cold War, in particular, led the executive branch to increase its power in making war without a declaration by Congress, to expand its secrecy protections, and to expand the use of Executive privilege.
Schlesinger also provides another concept: The Revolutionary Presidency, which seeks to stretch the power acquired through the Imperial Presidency into domestic affairs.
The founders granted the President extraordinary leeway in foreign policy because it was expected that neither Congress nor the public would be experts in foreign affairs. Indeed this has more or less proven to be the case.
Schlesinger uses Lincoln as a model for how Presidents might reasonably exceed their explicit constitutional powers in an emergency; critically, Lincoln insisted that his broad claims of power were specific to the setting, and thus should not be taken as a permanent expansion of the office.
Schlesinger also notes the tendency of Congress to move to reclaim its power after periods of strong executive power. (After the Civil War, after WWI, and momentarily after WWII).
The Cold War looms over the Imperial Presidency. WWII led to a resurgence of the Presendancy, with Korea pushing it to a new level. But Vietnam is the key war. Both LBJ and especially Nixon expanded the powers of the President immensely, particularly in its secrecy system (which Schlesinger intriguingly suggests is based on the false assumption of national security, but actually exists largely to protect the government from embarassment).
Nixon's creation of a large professional army also gives the Presidency extraordinary leeway in sending an army on peacekeeping missions and other foreign ventures quickly with limited oversight.
After Watergate, Schlesinger wondered if the Imperial Presidency was in jeopardy. But Reagan and, more so, Bush II led to a resurgence. Bush II relied on the secrecy system to an even greater extant than even Nixon.
JAH - Sydney Warren
"Richard M. Nixon, the author says, "for all his conventionality of utter- ance and mind was a genuine revolutionary." By his style and actions he defied tradition and made unprecedented assaults on the Constitution: his usurpation of the war-making power, his interpretation of the appointing power, his unilateral termination of statutory programs, his enlargement of executive privilege, his theory of impoundment, his deliberate disparage- ment of his cabinet, his discrediting of the press." [Warren points out that it is unclear whether Nixon's personality caused this or the national security state inevitably led to this.]